It means getting lots and lots of targeted anchor text. Your PR goes up if you get more links (simply put) so yes it does affect PR.
Its the act of pointing loads of links with a certain anchor text at a website causing it to rank well in google. "Miserable failure" is the most famous.
Recent and POPULAR GOOGLE BOMBING(as of 2004) examples are: Ladrones (http://www.google.com/search?hl=en&q=ladrones&btnG=Google+Search) (Spanish for "thieves") points to the homepage of SGAE, (Sociedad General de Autores y Editores), the Spanish equivalent of the Recording Industry Association of America (RIAA). The SGAE is an extremely unpopular association in Spain since they not only try to prosecute users of P2P applications, but also impose surcharges on the price of physical media such as recordable CDs in order to account for the theoretical losses due to P2P exchanges. Weapons of mass destruction (http://www.google.com/search?q=weapons+of+mass+destruction&btnI) - Internet Explorer Error look-alike joke page saying "weapons of mass destruction cannot be found". (Note: as of 1 December 2004, the joke page, although still available at [1] (http://www.coxar.pwp.blueyonder.co.uk/), had fallen to 20th place in the Google search result.) Similarly, Armas de destrucción masiva (http://www.google.com/search?q=armas+de+destrucción+masiva&btnI), Spanish for "Weapons of mass destruction", gives a Spanish version of the page above. French military victories (http://www.google.com/search?q=french+military+victories&btnI) - hoax, Google look-a-like page saying "no results found for French military victories, did you mean French military defeats?" miserable failure (http://www.google.com/search?q=miserable+failure&btnI), worst president (http://www.google.com/search?hl=en&q=worst+president&btnI) and great president (http://www.google.com/search?q=great+president&btnI) - whitehouse.gov biography of George W. Bush. Due to the search query of "miserable failure," the search terms miserable (http://www.google.com/search?q=miserable&btnI) and failure (http://www.google.com/search?q=failure&btnI) also point to the biography of George W. Bush. Recently, they've added unelectable (http://www.google.com/search?q=unelectable&btnI) to point to the biography on the White House's homepage. Interestingly enough, www.unelectable.com also points to the same page (despite Bush's win for his second campaign bid), and is second in Google's Search for "unelectable." See also miserable failure. With the addition of Google Local (http://local.google.com/local?sc=1&...re&near=washington+dc&btnG=Google+Search&rl=1) and Maps, searching for the phrase in Washington DC provides George W. Bush as the first result. litigious bastards (http://www.google.com/search?q=litigious+bastards&btnI) - homepage of the SCO Group, which initiated the SCO v. IBM lawsuit alleging copyright violation in the Linux kernel. bastards (http://www.google.com/search?q=bastards&btnI) also works. Jew (http://www.google.com/search?q=jew&btnI) - JewWatch, an anti-Semitic group, was for a long time the number one hit when searching on Google for "Jew", perhaps because of its linking pattern. The Wikipedia entry replaced it following a Googlebombing campaign organized by Daniel Sieradski, editor of the blog Jew School (http://www.jewschool.com). [2] (http://msnbc.msn.com/id/4767133/) [3] (http://www.jpost.com/servlet/Satellite?pagename=JPost/JPArticle/ShowFull&cid=1082606042155) [4] (http://www.webpronews.com/news/ebusinessnews/wpn-45-20040416GooglebombingOfJewKeywordContinues.html) Google added an explanation page entitled Offensive Search Results (http://www.google.com/explanation.html) and placed it in the sponsored link section. Buffone (http://www.google.com/search?q=buffone&btnI) - Silvio Berlusconi (Italian Prime Minister) biography. "buffone" is the Italian for "clown". Santorum (http://www.google.com/search?q=santorum&btnI) - "Spreading Santorum," a campaign to ridicule Senator Santorum by naming a mixture of bodily substances after him (see Santorum controversy). Out of Touch Executives (http://www.google.com/search?q="out+of+touch+executives"&btnI) - Used to lead to Google's own corporate information page. Out of Touch Management (http://www.google.com/search?q="out+of+touch+management"&btnI) used to work as well. Waffles (http://www.google.com/search?q=waffles&btnI) - Leads to John Kerry's 2004 election site, originated here (http://esoteric-diatribe.blogspot.com). Food Nazis (http://www.google.com/search?q=food+nazis&btnI) - Points to "Center for Science in Public Interest" (which advocates strict regulatory oversight of genetically engineered foods). Raar Kapsel (http://www.google.com/search?q=raar+kapsel&btnI) ("Weird Haircut" in Dutch) - Returns the biography of the Prime Minister of the Netherlands, Jan Peter Balkenende, who is known for his distinctive hairstyle. Gladjakker (http://www.google.nl/search?hl=nl&q=gladjakker&btnG=Google+zoeken&lr=) ("smoothie") returns website of Camiel Eurlings, the leader of the Dutch Christian-Democrat faction in the European Parliament. Searching UK domains only (http://www.google.co.uk) for poodle (http://www.google.co.uk/search?q=poodle&meta=cr=countryUK|countryGB&btnI) gives you a link to a Tony Blair biography (http://www.number-10.gov.uk/output/page4.asp). Velký bratr (http://www.google.com/search?hl=cs&q=Velký+bratr&lr=) (Czech for "Big Brother") - returns a biography of Stanislav Gross, the Prime Minister of Czech Republic. Ignorant Asshole (http://www.google.com/search?q=ignorant+asshole) returns the website of Cal Thomas. The reason was his column (http://www.foxnews.com/story/0,2933,140612,00.html). Déspota Cachaceiro (http://www.google.com.br/search?hl=pt-BR&q=Déspota+Cachaceiro&btnG=Pesquisar&meta=) return to website of Luis Inacio Lula da Silva, about the polemic New York Times article (http://query.nytimes.com/gst/abstract.html?res=F30E16FB3E580C7A8CDDAC0894DC404482). Old Rice And Monkey Nuts (http://www.google.com/search?hl=en&q=old+rice+and+monkey+nuts) returns the website of Herald Sun columnist Andrew Bolt. The phrase is an obscure reference to Tirath Khemlani, a Pakistani commodities trader who was involved in brokering an improbable US$4 billion loan deal to the Australian Government under Prime Minister Gough Whitlam in 1974. Khemlani was known derisively by his usual line of trade - rice and monkey nuts. As he was involved in commodities and not financial transactions as a rule, it was believed that Khemlani did not have access to the funds as he claimed but would attempt to obligate the Australian Government of the day to pay a huge commission for arranging the proposed loan. The bomb was perpetrated at the suggestion of Ausculture (http://www.ausculture.com) for reasons unknown. lying sack of shit (http://www.google.com/search?&q=lying+sack+of+shit) returns the Parliamentary web page of Australian Federal Attorney General Phillip Ruddock. This bomb was suggested by weezil (http://weezil0.blogspot.com) and executed by a number of Australian bloggers in protest of Ruddock's protracted political smear of the now exonerated Mamdouh Habib fuckwit (http://www.google.com/search?&q=fuckwit) returns John Prescott who is the Deputy leader of the Labour party government in the UK. He is the only member of the cabinet to come from humble begininings (he was a shop steward so rose to the top through the trade union movement) so is famed for being a bear of very little brain, hence the link. swivel eyed loons (http://www.google.com/search?hl=en&q=swivel+eyed+loons) returns the homepage of the UK Independence Party after the phrase - initially used to describe the party by blogger Anthony Wells - was adopted by several British bloggers.
Search Google for "miserable failure", and you'll see this "Sponsored Link" at the top of the results: Click on that link, and read all about Googlebombing... Cryo.