Keeping it for a while. The Thunderbolt is merely a sidegrade at best, unless you NEED 4G data speeds. The Bionic is likely to have an encrypted bootloader and will be a significant downgrade from the atrix if it keeps the pentile matrix for its screen.
Oh, and official 2.2 is hitting the Fascinate, and the source code from Samsung has hit the devs already, so I see more Fascinate goodness coming down the pipe one way or another. With the current superclean ROM I have on it, it's an absolutely incredible and enjoyable phone. I nearly always get a full day between charges, and I put it to quite a bit of use. Dropped calls are virtually non-existent, and for some odd reason with Superclean my GPS has worked EVERY TIME now. Locks in seconds. I've needed it quite a bit lately, too ...
Good stuff. I'm hanging onto it until I can get a dual core with HDMI out and not an encrypted bootloader. And hopefully NOT Bing.