I've found that i post different things to different sites,

twitter for on the go thoughts and random bits that don't fir anywhere else, sharing photos from my phone and links from around the web.

Google+ for talking to people i actually want to have conversations with not just random comments now and then. and for posting links to longer articles, and more political stuff.

facebook is mostly limited to updates to keep old school friends/acquaintances abreast of how/what i'm doing

livejournal is for long posts about how i'm feeling/coping/progressing

tumblr i mostly only reblog on, and it's almost entirely cute pictures of small animals, porn and stuff with HP/Glee/GoT etc

Fetlife is for keeping up with my kinky friends, occasionally there are interesting discussions, but mostly it's so i can see who's getting into relationships and when they post NSFW pictures.

those are my main ones lol, but i do use more! i'm a bit addicted to social networks i think