Help! Mac Boots in Safe Boot

This evening when I turned on my Mac it booted up in Safe Boot, and I'm not sure why. This is the 2nd time this has happened in less than 3 months.
The first time I googled to see why it would do that with no real answer. But, it did it again and I was hoping someone could help me out and
perhaps explain why this is happening.

If I restart my Mac once it fully boots in safe it will boot normally, but does anyone know why this is happening?
I always shut down normally and never let it run for days on end.

Here's my computer stats:
Mac OS X 10.6.5
3,2 GHZ
4GD
27 inch.

Sounds like you have a sticky keyboard. Have you tried to clean it or had a spill by any chance? Otherwise try Repair Permissions and Apple Hardware Test.

No sticky keyboard. It's almost brand new, only a few months old. And I don't drink or eat around it.