I have one, but all it does is parrot my Tumblr account. I don't check it, don't actively use it, and until I got the ability to parrot Tumblr posts, I didn't use it.

Reason being: Tumblr does everything I'd want to do with Twitter, but it's more flexible. I can write more, express myself. I don't see the point in small blurb updates, I don't care to post small, clever quips, and above all I find the interface bland after more than 5 minutes of usage. I tried Twitteriffic, but I had applications that do nothing but connect to the web.

EDIT: /unalone/