title: Using a sub-domain of website to login users
body: <p>Fogbugz-on-demand, 37 signals, and PB-Wiki all use sub-domains with custom url's for each group of users to access their login page.  So it doesn't even seem possible for a user using those services to login to a generc login (that any user of the service could log into.)</p>
  
  <p>At first I thought this was a terrible design flaw, but now I think this is a really good idea because of:
  1) Additional security, it may not be much, but you now need 3 pieces of info: 1 sub-domain url, 2 login, 3 password</p>
  
  <p>2) You can let the same login log into different accounts by the subdomain url.</p>
  
  <p>3) This lends itself to more isolation, load balancing, and easy deployment since you can have the subdomains running under different servers in more isolation from each other.</p>
  
  <p>4) You can gradually roll out changes to a certain set of sub-domains that are marked as BETA users before deploying them to all users.  </p>
  
  <p>Are sub-domain based logins for web applications the future?  Are there pitfalls with this design approach I'm not seeing?  Is it too confusing for non-programmer users to understand the sub-domain concept?</p>