The scale of information they collect. I am paranoid. Google and other web services collect a LOT of data and I'm just not comfortable with it.
While I do not intend to stop using _all_ services altogether, I do plan to minimize it as much as practically feasible.
This includes using my own email (yes, the web-host/ISP, as the case may be, have some degree of access to it unless I set up my own hosting server)
Sanitising my search queries along with using random rotation proxies if possible. perhaps use TOR. This will depend on acceptable speed achievements. If it is too slow, I will think of other ways.
Blocking all _known_ google (and of course other services too) tracking applications, viz. Analytics, Feedburner, Adwords, Adsense etc
Personally, I'm planning to get rid of Google in my life. Entirely. And Feedburner was just the first step