By side projects I assume you mean web apps and programming related things. I've pondered a system to track these, but it would be even more fascinating to extend it beyond code - think: artwork, carpentry, electronics projects, robots, etc. Basically a 'Things I've Made' kinda site.
Edit: Interestingly, the thing about side projects is that most of their value is derived from what can be learned while building them. Often they simply die upon completion (or when boredom sets in) because there isn't much left to learn from the project. Because of this, I don't know if there's necessarily a personal benefit to archiving your own projects online (other than showing off / clout / credibility for resumes and such), but I can definitely see value in the social building part of it - which is probably the goal anyway.