Does Google have any guidelines on tracking cookies or tracking pixels? Can a site drop too many cookies?
To the best of my knowledge, there aren’t any guidelines as far as having too many tracking cookies.
If you do have so many tracking pixels that it starts to slow down the user, or if you do so much tracking that you get written up in the Wall Street Journal and people really don’t like you, then that might have an effect on your business.
Cookies can be used for a lot of different reasons, sometimes for tracking, but also for storing preferences and a whole bunch of other stuff. To the best of my knowledge, Google doesn’t make any distinction on the number of cookies, or if there’s a whole bunch of little one-by-one pixels that are on your site. So that, to the best my knowledge, is not a factor in Google’s rankings.
by Matt Cutts - Google's Head of Search Quality Team