It depends upon the application. I run a semi-popular forum, so I require email addresses to keep the ban evaders, trolls, and spambots out. If you think you're

It depends upon the application. I run a semi-popular forum, so I require email addresses to keep the ban evaders, trolls, and spambots out. If you think you're going to have problems with the former two, keep the email requirement. However, if you're not doing a community related thing where everybody has to play nice, like a service app like Basecamp, feel free to not require it.