I discourage it. People will always look for you (and worse still, send you mail) at the dot com. And there are lots of decent dot com names still available.
Guess who got a bunch of dirty looks the next day for sending a co-worker to a porn site?
Eg. searching for 'python' gets you python.org as 1st result. You don't want to go to the .com
Also, I wonder how many people (say, someone's boss), heard about this cool Python language and just tried python.com. Oops.
Somehow I also remember it's php.ne, not .com, even though I haven't visited that site so much lately.
But both of these were already an established internet brand when I started using them.