I've been using it for about two hours now. It definitely has some bugs, some of which have already been mentioned here.
I can understand MMS not working, most likely cause my iPhone is not setup for it with ATT.
I wouldn't say there aren't any features that aren't working, I for one am really liking the wide keyboard for emails and texting. Copy and Paste so far has worked quite well for me.
My only real annoyance thus far is that, texting can get slow at times, sorta like how texting slowed down when my phone was jailbroken a few months back.
BUT, if you're going to spend 99.00 just to get the 3.0 Beta, I would really give it some thought. Unless money grows on trees for you, I wouldn't do it. I got a friend to add me on his developer account.
I'll give it a good week's worth of use before I decide to downgrade back, hopefully I'm still able to.