E-mail addresses are bitches!
There, now that is said I can tell why.
Should you ever have time on your hands you should read RFC 2822, it provides an interesting (though somewhat dull) background into e-mail messaging. Alas one can also see why it is so hard to validate an e-mail address, it is an extremely flexible [...]
There are those things you encounter again and again and again. Generating passwords is one of those. My experience is that whenever an application needs to be created which deals with user account creation, it is best to let my application create a password for the user.
Why? Simply, I am lazy.
Good developers and users alike [...]