I'm having exactly the same problem -- my iPhone 4 sync is hanging up at the "downloading safari safe browsing data." It just never progresses past that point. The point of the question really isn't about turing off this feature; it's about the problem of the phone NOT syncing properly. Why should it be necessary to turn off this feature in the first place in order to sync the phone?
Ever since upgrading to iOS 5.0, I've noticed all sorts of syncing problems with my phone. Everything in my calendar was duplicated, so that there are two of EVERYTHING, past and future events both. And now I really can't sync at all (although I'm getting ready to try to turn off the "safe sync," if I can ever get the current sync to cancel).