You know, being involved in sites daily, I have never been able to get involved in these such sites.
Ironically I have to create some just like that and I don't know... I just don't seem to want to go on them.
Most of them are overpopulated sites with many immature fuckwits who will do anything to bring said site down to its knees. I have my selection of sites I visit, and I don't need something amassing all of them together. I find it just clutters the way I browse the internet. Maybe the odd time I go onto Youtube to check on something, or onto Digg to see a specific article, but I just don't find myself getting attached.
I tried Twitter, it failed. I tried Facebook, it spammed me with emails.
Last.fm is the only site I really have respect for in this new era of cool sites. Well, last.fm and maybe netvibes. But then again, I only really go onto them if I desperately need something.