I recently started browsing the excellent UI-patterns.com site again and came across one of my favorite UX concepts: Lazy Registration.
I won’t repeat the details too much here, but the concept is simple… let your users use you and delay making them create an account until the last possible moment. A lot of sites can benefit from this… I know I’ve felt largely frustrated when I’ve had to register just to search a public forum, and all too often I hear of people wanting to lock down their sites like no tomorrow in the name of security… and nothing could be worse!
The more people can use you, the wider your user base is. 
