Now, I have an awesome friend circle for KHR who I mostly think of as a Plurk circle (since that's where we mostly congregate), but Plurk is much more of a behind closed doors kind of place than Tumblr or LJ. I think of Plurk like an improved version of a chat program mixed with a blog like LJ/etc. (actually, Plurk is pretty awesome. like Twitter, but way better for interactive communications), and it's wonderful for holding conversations with people and commenting about my daily goings-on -- better than LJ for that -- but it kind of sucks for like, fan essays, or long involved public ramblings, or that kind of fandom interactivity?
And, yeah. Tumblr. Same caveat I said before. Tumblr is good for some things, but I am tsun at the fact that it seems to have replaced LJ for a significant amount of fandom blogging. It's great for posting interesting shit, but having to reblog a million times just to share back and forth comments is terrible.