The untucked shirt - yes or no?

I've just been reading an American blog on whether men should tuck their shirts in or not. Granted a lot's going to depend on what sort of shirt - some are cut to be left hanging out - while others are more neutral.

So, Tees or formal, polo or with collar stiffeners - your homework for the weekend is to tell me what you think, should men wear shirts that are hanging out or not?

(That other blog post is here, by the way).