I tried downgrading last night. It did not go well. I ended up restoring several times, including having to restore as a new phone - after which I discovered that for some reason none of my backups would work. Eventually, I had to restore a backup from February, which means I lost a lot of changes.
Most of it has now been resynchronised, apart from the fact I can no longer login to WoW as my mobile authenticator got removed. I have reinstalled it, but my account no longer recognizes it. I have emailed Battlenet support, but no WoW until they sort that out.
I feel disappointed and angry that Apple have so obviously ruined the 3G phones as a cynical sales ploy - hoping to force happy 3G users to discard what was a fully working phone and buy a new iPhone4 - which they neither wanted nor needed.
Of course, the fact that none of the shops have them in stock anyway, due to Apple once again restricting the supply in order to increase the cachet of being able to buy and own one only adds to the fact that £400 worth of kit only 18 months old is now slow and hard to use, whereas last week it worked fine.
Apple seems to forget they already have a large number of almost fanatical fans, who are likely to upgrade eventually anyway - so this sort of tactics are not necessary.