I'm in the same position, even though my iPad's not arrived yet I'm deciding if I should JB or not. I had a iPod touch 1G and Jailbroke that at the start, but that was only because it had just came out and there was no app store. Now, I'm thinking I will just wait.. as it is I haven't used iOS for over a year so there's probably enough to keep me satisfied until iOS 4
You'll want to jailbreak once Flash is released..
Is it possible to retrieved my blobs from Cydia. I really wish to know more about that subject. Any links ?
Do it! If you don't like it, restore. If you don't try it, how will you know?
iOS4 has no jailbreak available, therefore you can't try and then restore if you have already updated.
If you have iPhone 3.1.2 or 3.1.3 then jailbreaks are available, and so far as I know, when you select restore in iTunes it restores your phone to the OS present in your last backup.
If I am wrong, could someone please confirm, but I don't think iTunes forces you upgrade to iOS4 if you do a restore.