They say you cant cloak pages, and hammer anyone who does it, except the NYT. But if you google "cloaking software"... There is tons of Adwords for it.... Make money then watch their IP address (New Google monetization model)
It's buying links for SEO purposes. Which google, does not sell, they sell traffic. You can still buy links for all the traffic purposes you can afford. If you want to purchase for SERP(s), PR, etc, then you be punished. How they can distinguish between the 2, I forgot where I read it, but they had some interesting ways to distinguish. Actually I believe it is worded to "avoid cloaking". The problem is, most people who use cloaking, are using it to trick a search engine for higher rankings. If you use cloaking to serve your user with personalized and higher quality - targeted content, google will not bother you (as you can see with NYT).