Apparently it's pretty common for folks to mistype web addresses and leave out the dot before the name of the site. The result is, you end up somewhere other than where you've intended to be. It really isn't that big of deal, but hundreds of lawsuits have stemmed from people hoping to capitalize on the mistakes of others.
Facebook is the latest to fend off from any such advances by purchasing the domain, wwwFacebook.com. The domain name became available in late May and it's now listed as the property of Facebook, Inc. No details on the sale or exchange are mentioned accept that Facebook acquired the domain through MarkMonitor brand protection company.
Apparently, Google went through some type of legal arbitration to gain rights to their alter-address back in 2007. Twitter also had some kind of legal battle over misuse of the wwwTwitter.com domain. So, I guess Facebook just wanted to avoid any non-sense by taking advantage of its availability now. We'll keep you posted on anything that happens with the space.