OK, so if PPC can be scammed, why shouldn't Google offer a timed ads rotation. Basically, they rotate ads now based on click count, but since that can be exploited using proxy servers (a proxy server can simulate a click from almost any number of sources), why not use a time x position x frequency rule? Seems it would keep things fair. The value of the search term would be determined by the search frequency, which could also be manipulated, but that would be more difficult. Um, and I wonder if google puts a cap on keyword phrases, or repetitions... probably. I don't think multiple includions of a word should trigger spamming, rather, the indexing method should ignore repeated content.
I think rotating their ads would have some many advantages, for google and marketers. First, it would (somewhat) level the playing field for newbies. It could bring at least a baseline of traffic... say 100 visitors a day... to start. Rank wouldn't be the end all, be all. Second, page rank wouldn't be as traceable. I think a lot of the SEO software out their uses page rank as part of their analysis. Seems Google would like to confuse the software, right? This would do it. So, maybe you want some results always on the first page, OK. Maybe for the major keywords, page one can be more closely scrutinized, - a lot of work, but Google has the money. That's just an idea though. Would it require more or less computing power? Umm, I think the algorythm could be simplified some, so it might balance out. Or not, I don't know...
Google already has their own method for rotating and ranking ads.....You can also choose to have your ad show until your budget is done for the day or have them show it even over the entire day...