My go to ROM
I know this is a bit late, but while I try other ROMs I keep coming back to Phiremod 3.0.2 (not fusion). Sure, it's based on an old version of Android, but the Vibrant is also an old phone, and it seems to be optimized to heck.
I get 3-4 days of battery out of normal use (much less if you ever run Minecraft PE, but that's universal) - and that's freakin' amazing.
It's quite smooth - I compared it side by side with a stock Galaxy II last week, and for normal use a Vibrant with Phiremod compares quite well. It's very stable. Things seem to be well arranged.
And it's quite tasteful - I can't let my colleagues or lady friends see some of the other super optimized ROMs I've tried that are skinned to look like teenage boy's Myspace pages (looking at you, Toxic).
So thank you for this!