Social Networking Sites

I'm a newbie when it comes to social networking, so it is really hard for me to comment on SNS out of experience. I've logged to MySpace few minutes ago; opened the account with Twitter a week ago; own a Facebook profile for few months but rarely use it. The only SNS I really used is a polish site http://www.nk.pl/ When the nk.pl was created I was really excited. I was among the first million people who logged on (Poland is a 40mln people country). Initially it was created for schoolmates, to find each other. That is how the website got it's name "nasza klasa" or nk.pl ; it means literally "our class". I was thrilled to be able to find people I was close to for 8 (primary school) or 4 years (secondary school). Initially I logged on every day. Then I realized that it really takes up a lot of my time. I don't negate the fact that it was really nice to see all those once familiar faces, to learn about their children all other things; but somehow I lost interest in it after a while. SNS are an interesting initiative but with work, study, commute and overall life, logging onto SNS is not my daily priority.
I can say very little about the other 3 SNS. I'm still learning to socialize thru the Twitter or Facebook. With T my biggest challenge it to squeeze my thoughts into those 140 signs :) Facebook ahs LOTS of potential for me but I'll need to get used to logging there more often. As for MS, the minute I logged on I got suggestion on whom to befriend and but about 75percent of those suggestions were commercial account...so I know that MS won't be my favorite site anytime soon...