Which social bookmarking site is effective at the moment

I'll be honest with you, I use Facebook so little it's hard to remember, but...I know that it has options in your profile for Digg, Twitter, and other bookmarking and networking sites that you are member of.

I think I just filled all that stuff out, and it auto updates what you do online....what you bookmarked and such. I am sure there is a box you have to check, but just look around in your profile and settings.

Wish I could be more help.