Suggestion for a Signup Plugin

How easy/hard would it be to create a plugin that modifies the signup to allow users to set their own password ?

The thing is that my future users will mostly be internet noobies. Going back and forth between their email and my site will be a definite problem. Not to mention required emails being eaten by their spam boxes ?

I think this is a very needed plugin. The only other mu site I saw that had this besides wp.com is that new shopping one.