If undecided between evo and vibrant, watch video.

I've had the vibrant since day one and I've had some lag issue and last night it got really bad. so this morning I did a factory reset and did not put back all the apps that I had before
Its working a lot better now. Im sure I had a bad app or two. You have to remember that this is a new phone and it will have some issues. Give it some time and I'm sure samsung will do a few updates. I know they are working on one for the gps problems. The evo had some updates I'm sure. Look at the droid x it had two before the phone even came out so be a little patient. If its so bad you can't do anything then take it back.there are going to be bad ones. My first one had a bad speaker.
 
I'm not sure if you are willing to try this but at another forum they said doing a hard reset fixed their issues.

Chances are high that a poorly written app from the market if the culprit which is why the reset fixes it. My Vibrant runs flawlessly but when I first got it I installed an app that made it super slow. I reset the device, started from scratch and didn't reinstall the application.

Now it runs with no issues lightning fast.