Enabling private browsing in Mobile Safari is a chore, because you have to exit the app, go to Settings, and enable it from there. There's actually no way to enable private browsing from inside the app itself, which is kind of lame.
Wouldn't it be better if you could enable private browsing quickly from the share menu in Safari? That's the exact premise behind Privata — a new jailbreak tweak that's available for free on Cydia's ModMyi repo.