I didn't see this posted and I know there are a few Vibrant owners here. A GPS fix has been issued over Samsung's Kies software. After the fix I get a lock within 10 seconds and it's been pretty accurate so far.
http://phandroid.com/2010/09/29/gps-update-now-available-for-the-samsung-vibrant-through-kies/
http://phandroid.com/2010/09/29/gps-update-now-available-for-the-samsung-vibrant-through-kies/