[eluser]MadZad[/eluser]
Also keep in mind the situation where a user loses their email address suddenly, like switching jobs or internet providers. Be sure that these folk would be able to change their email addresses, whether or not you use them as logins. I remember encountering a company that required confirmation to the email address on record in order to modify a profile - including changing email. Duh.
A reason you'll hear a lot of good advice, sometimes conflicting, is because there are different solutions for different user bases. My advice would be to leave the computer, grab a beverage, forget all about programming, and envision yourself as your users. Then think about the ways they'd interact with your site/application. Sketch out a few page flows with good old paper and pencil, then run through the flows in your mind with a user's mindset. If you get annoyed, improve the page flows. Works for little details like whether or not to use email as a username, and much bigger issue.
Good user centered design also makes for a lot less maintenance programming. Then again, bad UCD is useful to keep the customer base low...
