People spend lots of money on adwords, but the point is how much altering the serps would increase that amount.
Put it this way, if today was AFTER the IPO, perhaps a case could be made, but as of now, Google’s product value is quality results. I can’t see how anybody can not see what penny ante nothing adwords is compared to the IPO. Suppose Google’s value even goes down 5% because of crappy results… that would be about a BILLION dollars. All adwords put together between now and the end of April (the late first quarter being thought of as prime IPO time) would be a drop in that bucket. And that is only looking at a 5% drop. And that is all adwords put together, not just the difference between what difference in adwords revenue they could get by screwing up the results.
Google has much bigger fish to fry. There isn’t one in a billion chance right now that Google would intentionally hurt the quality of their results right now.
Also, there are lots of valid reasons to crosslink. Penalizing is different than ignoring, and ignoring is different than dampening. I don’t see any value in Google penalizing. Ignore, maybe. Dampen, sure.
There has never been any evidence of a filter. All you have to do is look at the old results, the post-florida results, and the current results. At the same time that some sites disappear, some sites that ranked 3, 7 and 12… might have gone to 1, 20, 5… might have gone to 4, 8, 2. Obviously there is no filter otherwise the relationship of those sites to each other would not be affected. There is just a much different ranking algorithm.
Google tells people what good SEO tactics are, and what to avoid. http://www.google.com/webmasters/