I tried to restore to iOS 5.0.1 when I wanted to sell my iPhone off but ended up restoring to iOS 5.1 because of the 3194 issue and nothing can be done. Tried everything on the web
You could have ripped your APTicket from your iPhone 4 with iFaith, then restored to 5.0.1 using the saved APTicket. You'd have had to done this before you installed the 5.1 firmware, though.
As for everyone else talking about jailbreaks being buggy, I've never had any problems other than one minor issue with icons occasionally (maybe one icon every week or so) appearing white, which can be fixed by a reboot or respring. If you guys have been having problems, I can almost guarantee you it's because you installed a faulty tweak or something went abnormally wrong during the jailbreaking process. And even if you install a bad tweak (which I did a couple days ago), as long as you have Mobile Substrate, you'll be able to remove it without much difficulty. It's also worth noting that when bugs are found in the jailbreak, they are very quickly fixed through Cydia updates.
And on the topic of un-jailbreaking, I don't believe that Cydia does this, but some jailbreak apps save settings that iTunes will back-up and restore, though the settings won't affect your iDevice in any way if the jailbreak app is not re-installed (other than eating up a few kilobytes because data takes up space).
[My apologies for necro-bumping this thread, but there's information that hadn't been brought up]