The Samsung Vibrant and Captivate are all around great phones — the Galaxy S phones in general are — except for one teensy weensy little problem. The GPS has been known to go a bit bonkers, give inaccurate location, or just plain not work from (most of the) time to (most of the) time. A software update fix was issued to help resolve the problems, but if for whatever reason your GPS is still failing you on the Galaxy S handsets from T-Mobile and AT&T, Samsung has provided some helpful tips to get you through.
Check out the guides for more info on solutions, such as the use of GPS Restore.
Guide: Samsung Vibrant
Guide: Samsung Captivate