My hunch is that "short, and pronounceable, is preferable", but other than that, I think there is a sufficient number of examples (including the ones you mentio

My hunch is that "short, and pronounceable, is preferable", but other than that, I think there is a sufficient number of examples (including the ones you mentioned) to make the case that a web site's domain name need not be descriptive of the site's service or content. The challenge is to do whatever it takes to build up name/brand recognition, but I think that would be true regardless of what sort of name you went with.