WSJ writes about an analysis done by Dennis Forbes:
All of the 1,000 most common English words have been snatched up. The word “a” appears more than any other, though most of the time, of course, it’s just a letter in a longer word. The least-used common word is “consonant,” Mr. Forbes says, which is in just 42 domains, including “consonantpain.com,” which isn’t a misspelling but a word game.
Half of all domains are between nine and 15 characters long; the average length is 13. A domain can have, at most, 63 characters, and there are 550 such domains. In fact, some people have made a haiku-like art out of 63-character domain names.