As promised, it seems that T-Mobile's version of the Vibrant is getting Froyo today after a brutally long wait. The good news is that you won't need to wait for a staggered rollout, apparently -- but the bad news is that currently you'll need to get it using Samsung's Kies Mini PC app, not over-the-air. Tethered updates are always less convenient than their OTA equivalents (though Samsung continues to be particularly fond of them), and in the case of Kies Mini, there's no Mac version, so you'll need to be near a Windows machine to make it happen. This hasn't been officially announced yet, though commenters over on TmoNews appear to be having luck -- so if you give it a go, let us know how you fare.
Update: T-Mobile's official FAQ on the update is up -- so yeah, it's official!