Most tracking is done via query string anyways. (the ?yourid or =yourid etc in the url)
This will only affect bookmark signups with sites that use ccbill tracking and other similar things. (Where you bounce the user off of a tracking site and then back to a static url afterwards)
People who signup right away will still be tracked regardless of what type of tracking is done.
The privacy mode just clears everything out once you're done...it doesn't block things as you are surfing. You wouldn't be able to check your gmail or myspace or anything like that if your browser didn't accept cookies.
