URLs are dead
I agree with some of Darren's discussion on choosing a domain name...but URLs are dead. People type stuff into Google. They've learned not to trust bookmarks (broken computer, switching machines, home vs. work, too many becomes unwieldy to find), but can easily memorize search phrases that get them where they want to go.
James related how his wife finds recipes by remembering (again) the search phrase plus the position on the page. And of course, if you are on the same computer, the link will be purple, showing that you've visited it already.
The only reason you need a "good" URL is for offline marketing purposes. But even there, people are still likelier to remember the name of your company, and just type that in (because sometimes it's not .com, it's .ca, or some other reason). Bottom line: Google/search is easier for end users. So optimize your site
(I wish those bullets were numbered on Darren's post -- let's just pretend they are). In any case, we couldn't do rule #2 without breaking rule #1. There are a very limited number of 5/6 letter domain names left. So we opted for hard spelling. At least it's still short enough to spell over the phone.
For #5...I agree about punctuation, except that for branding, that's easier to read. And when you type "tigh na mara" into Google...they're the number 1 hit. Mission accomplished. Same with drupal-world-domination.com (coming soon).
And I'm calling bullshit on your repeat visitors comment. If people can always find you online (email notification, RSS feeds, Google search for your name/business keywords), that's what will bring in the repeats.
Update: while I was typing, Richard also responded -- In the Future, Domains and URLs Won't Matter -- and Darren updated to include some of those thoughts.
Update 2: I like this phrase I used in Darren's comments (which have some good back and forth between him, myself, and Richard), so I'm keeping it here, too:
Ten years could be enough time to move to an all-search based front end to the web -- only machines will need to know URLs, just as only machines need to know IP addresses today.