If you're familiar with Basecamp or Backpack (both from 37signals), you know that when you sign up you're given a special URL to login to your account. It's usually something like "username.backpackit.com."
Let's say that you haven't used Backpack in a while and you go the homepage and find the login link (which is tiny and easily missed) but when you go to the Backpack login page, instead of a login form, you're given instructions about your login URL.
Personally, I've never liked this system. I don't use Basecamp or Backpack very often and always forget to bookmark my login URL and am always frustrated when I can't login from the login page.
Tonight I was trying out StikiPad and found that they give users a login url, but they also allow you to login right from their homepage.
I'm a big fan of 37signals, but on this point I think StikiPad does it better.