A few companies (justin.tv, drop.io, del.icio.us) have pulled off not being a dot-com, but this required creativity and great marketing.
But one anecdote (and I'm sure del.icio.us has a dozen), I know PC World magazine wouldn't have misspelled our site as "bug.BD" if we had been a dotcom. (They did get the url right later as bug.gd, even if they got our "product name" wrong.)
I guess the upside is we get a free mention in the next magazine when they correct that.
Fun!
also, in the very beginning when I was using delicious I'd type delicious.com instead of del.icio.us. It's just harder to remember a name like that O:p