Regardless of whether a privacy policy makes you feel comfortable, their ability to observe all of your browser activities is difficult to ignore.

A rogue employee spying on people (happens a lot, we read), or the company accidentally saving your data and then being hacked, or any number of other potential privacy issues... probably isn't worth the small amount of money you might be able to save sometimes. At least for me it's not.

On the other hand, all but the most careful internet users are probably giving away nearly all of their personal information and records of their activities anyway, so maybe it's a moot point.