Aside from Orkut, there are a slew of social networking sites that:
- are 100 times faster
- have TONS more functionality
- have significantly more potential, given their structure
- have management with more of a sense of humor, yet still manage to keep their sites useful for business-networkers
I guess it really is the "well, all my friends are on [x]" syndrome, a la AOL/AIM. Similarly, there are many other more robust instant messaging solutions, but AOL/AIM is where "all your friends are," so, well, there you go.
Given that Orkut.com is supported by Google, though, and so much of Google-touched stuff becomes successful... I have high hopes for it ;)