I just had it happen to me. I booted up my phone with the middle finger of my right hand on the power button and my thumb on the left... So if you can picture it my whole hand was over the phone. I'm sure I brushed one of the buttons at the bottom while I was trying to power up single handedly.
I did a search on google and came up with this thread and came up with another site that said you get into safe mode while holding the menu button during the power on. I just tried that again right now and it does not appear to work on the Fascinate, on the other hand I'm sure I touched something while I was trying to power up or maybe I touched the menu button while shutting down.
I'll play with it another time. I need to get to bed.