If you use blackhat seo tactics it's very likely that you will get banned. Many times a site is banned because of a user's report. When get banned you get 0 pagerank on your page and you can not be found in any search. This does not mean that you get removed from the index, but you are not visible to any competitive keywords. If this happens to you, you will get a notification from webmaster tools. Go check those tools and the Google's Guidelines. You might find them very interesting.
yes they are showing out there but if this happened to my website, i think i should clarify google about my website purity and send him the reconsideration mail.
they do exist, but as far as i know there is no list of what they actually are and how long they last for. I think it's more of an internal measure that google use rather than a published measure for website owners
From what I understand Google penalties include breaking any of their webmaster guidelines~ http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=35769
It would be a God Send if penalties were to show up in Google Webmaster Tools. A lot of webmasters make honest mistakes by copying techniques from successful websites and are sometimes confused when they make these mistakes and get slammed. Most of us want to play by the rules and would if the rules were better defined. A good example is linking, cross linking and sitewide links. There alone are 3 Categories right there that Google is all over the board with as shows no really consistency. In real estate it is quite common to see successful websites in major markets heavily engages in cross-linking, three-way linking, sitewides and home-page link exchange schemes. I know that some of this has been brought to Matt Cutts attention in the past and it may or may not be addressed in the future. Either way, a little clarity and an equal playing field would be appreciated. We all try different things over a period of time to improve rankings. A transgression against the Webmaster Guidelines may not be discovered by Google for months. Then when you do get penalized you scratch your head and try to figure out which one of the 10 things that you have done got you in the “Google Penalty Boxâ€. Generally, the first thing that you undo is the last change that you made to your website. Unfortunately, that may or may not be the problem that got you in trouble. So YES, I would love to see notations or infractions appear in my Google Webmaster Tools CP! Now if I have misspoken about anything in this post, PLEASE correct me. Just my 2¢ worth, ~Mack