What do I have to do to unjailbreak from Absinthe?
To jailbreak with Absinthe they tell you to erase all data just because the software works faster, but you can do it with all your info. It will only take more time.

I recommend you to use the last version of Absinthe.

To remove jailbreak you have to restore your idevice. (it will restore with the last iOS version at the moment).