This post was prompted by a user here being found out by his SO, even though he was on a throwaway account. There are 2 ways I would recommend to create the user part of a throwaway:

  1. http://units.d8u.us/rand?type=string will generate a random string 22 characters long (the string: field). This is your new username. Save it in keepass or similar. The service is written by a cousin of mine, and he's a privacy nut, so he's not going to note down your IP address or any personal information. If you don't trust me, the service is open source for your auditing pleasure.
  2. http://mailinator.com lets you create throwaway email accounts. Grab the username of the suggested address (i.e. DarlingTinkerton) and use that as your username.