When I first saw it, the address bar stood out massively. It looked useful, since you could pretty much search with it, but it was garishly ugly. Luckily, "oldbar" lets you go back to the original design of the navbar with the search-y feature still intact. It's beyond useful and I now can't stand using IE, which obviously doesn't have it. That said, I do notice speed problems with it at times as it loads my history though they're much better than the overall speed problems with IE when you turn it on =P Anyhow, that's besides the point. I'd say that F3 is worth getting just for the new address bar, which is pretty darn awesome. There are some other cool new features too, but they hardly compare.
