This effects nonprofits if you have a Facebook Fan Page.
Last night at 9 PM, Facebook usernames opened up to the public. You can grab a vanity URL for your Facebook profile or page. I selected http://www.facebook.com/beth.kanter. It's like getting a tatoo - you can't change it. Here's some advice from Mashable.
Facebook pages also have the option to register usernames, but as Mashable reported, your page has to have over 1000 fans to quality. Otherwise you’ll have to wait until the end of the month to register a custom URL. Well, I have don't have Fan Page, but have been thinking about setting one up just to play with it. If you're in that position, here's some useful information.
Beaconfire Wire: Facebook Vanity Urls - Not Just for Narcissists!