I've tried using Tumblr, but I'm just not a fan of the website. I might give it another try one day. Other than that, the only other thing I actively use is Twitter.
You should add Skype to the list. It's one of the most popular programs out there..
One thing I don't understand the appeal is, is Tumblr. It's pretty annoying trying to talk to people on it, because you have to reblog stuff just to communicate. I use it to post my artwork, but otherwise it just seems kind of pointless to me.. or I'm somehow missing the point of it.