title: How does Facebook pre-empt URL extensions it needs in future?
body: <p>I've been reading a lot recently on building community based applications, and when it comes to giving your user accounts 'cleaner' URL strucures, most are of the opinion that the user accounts should have a structure such as <code>example.com/user/username</code> rather than <code>example.com/username</code> which makes a lot of sense with regards to how mod-rewrite will handle the URL and serve the correct page with minimum potential problems. This ofcourse also helps in planning/ organizing file structure on website and future-proofing needs such as when later you will have your <code>example.com/blog</code>, which will not be taken by an existing user.</p>
  
  <p>But the user-experience designer in me still wants to have the <code>example.com/username</code>. I'm just wondering, how did Facebook, Twitter and such applications pre-empt and reserve the URL names they would need, assuming that they did, so that they don't have issues with these years later, like today?</p>
  
  <p>Did they pre-empt and reserve to themselves these extensions? Were they just lucky? It beats me.</p>