I just deleted my tumblr account because it kept fucking up. The biggest one? Tumblr won't support anyone who uses "Missing e," which is the best browser extension for Tumblr because it adds more functionality than the tumblr developers know how to read, for any reason. So, say you email the tumblr support team about a URL issue but you have Missing e installed. They won't be able to help you because of your browser extension. This is almost as bad as if you had an iPhone and Apple couldn't replace it because you turned iCloud off. It's asinine.
The second biggest reason I deleted it was because I kept getting random posts posted to my "blog," if you can call a tumblr account a blog, that I never posted. So, either someone hacked my account and Tumblr had no way of knowing, or tumblr is just fucking retarded. I'm going for a bit of both, because even Facebook is smart enough to add location tracking to their user's logins so nothing goes wrong.
Tumblr, if you fix these things, I'll THINK about coming back. But I probably won't because Blogger is a lot better and they're nicer.