Some orkut observations:

I got on the other day, by the count algorithm (uid from 1M), I am user 6617. My last friend request earlier today has a user of about 23K. It will be interesting to see the growth curve of the ‘invite only’ network
Everyone on my current friends list is a blogger (also the biggest community I am in is ‘Bloggers’ which was at about 2 or 3 when I joined; now grown to 235)
The system looks like it’s written in C#/ASP.NET; it uses a lot of xmlhttp for inline page updating (works in IE, Mozilla, fails silently in Safari)
There’s a level of privacy control (restricting information by predefined, but not arbitrary groups)
You can add someone as a friend automatically, which is then pending. If you are rejected, you can’t add them again, they can add you; I’m assuming if you reject them it’ll mean you can never add each other, but I wasn’t really feeling like testing that part out
There’s some ratings; you can be a fan of someone, and rate your friends (aggregated pseudonymously) on trustworthiness, coolness, and sexiness