I just read Alex Miller's blog entry where he states quite nicely why unit testing even very simple code is not dumb. He posted because of Eric Burke's excellent discussion of the matter.
I really don't have much more to add, except to add one more voice to those who state that unit testing seemingly trivial code is important. I will say that I've actually caught silly mistakes (like failing to set a field to the correct value in a constructor) with simple unit tests. Also, writing tests for such code lets me spend more time thinking about the hard parts of the problem and less time examining 'simple' code to make sure it is correct.