This can happen whether you're rooted or not. Personally, with as many different ROMs as I try on my phones, I expect this daily, and experience it weekly.
However, if you have not rooted (OP) then watch your phone carefully - if it happens again, you need to start looking at your apps, b/c one of them might be doing something stupid on your phone.
If you are rooted, then double what I just said - root access allows you to do things that you normally cannot do - and that means messing with system files and such, which can have dire consequences.
I am not saying this is a direct cause of rooting - I always prefer to test a system first and then make a determination, and 99% of the time it is some app or another being stupid. A lot of the apps in Market, although they don't actually say it, are, in fact, Beta-level apps, meaning there are bugs, inconsistencies, and flaws that need to be worked out.
Comes with the territory.
basically, if it doesn't happen again, you're cool. If it happens very occasionally, you'll need to dig deeper and see if it is an app. If it happens frequently, you need to look now and figure out if it is an app or if it is your phone. And if you just got your DROID and are still within the 30 window, forget troubleshooting, go get a new in-warranty replacement and be done with it.
(If you're within 30 days of purchase and they offer you a refurb, DO NOT TAKE IT - demand a new one.