I started using orkut about 2 months ago. My experience is that it is PAIN to use orkut. Honestly, 8/10 times you get an error when you click on something. I was just trying to post something and after 10 trials, I got tired and stopped. It's too much frusturation...
Having used other Social Networking sites like Yahoo's 360 and Microsoft's Wallop, I think I clearly see the pluses and minuses now. I actually posted a lengthy suggestions list on MS Wallop Team's page. Somebody thanked me for suggestions but I don't know if they will implement them.
Basically the big advantage orkut has over the others is that it has 'communities' (or forums). That is where people meet others and I believe that's why orkut is so populer. I mean it really rocks when it works. Unfortunately that is not the case most of the time.
One may ask what does it have that yahoogroups do not? Interestingly, not really that much. I believe yahoo can do some magic to make 360 work like orkut.