The downside is that browsing the web on a service like that sucks ass. Tor trades off some security for a basic level of user experience.

Sadly, modern web design makes stuff like WWWoffle less useful than it used to be. Plus it's difficult to set up fully anonymous services on the far side of the link, I mean you're using Tor for a reason, and leaving breadcrumbs on the far side of the network is risky.