Having used all major social networks Orkut, Facebook, Twitter and now Buzz, are these really useful?
Does what it's meant for. Not too much of sharing. Privacy level is great. Days where anyone's scraps can be viewed is gone. It's not actively developed or it has reached an point there aren't room for sharing. Google prefers twitter way of doing things, being public.
Has better UI than Orkut. As it turns around, FB want's to be God of all social stuff, which brings down the comfort level. And too much of sharing. Looking at the default news feed, it's all spam i.e. basically stuff I'm not interested in. Especially crapville games were annoying. Overall it has got big, there can only be downfall.
Doesn't care about our personal information. All the links and thought we share matters. Simple. Real social network of all. It's not about friends but about interest.
Worst of All
Applications that link these so called networks. Specially hate apps that tweet in FB/Buzz. And hate sharing news in these networks. Better use Google reader.
Twitter to be social. Orkut/Google to share with friends & relatives.
To address if these networks are useful or not, Gmail & Picasa gets the job done at the moment. For all public stuff Twitter is the best.