Pro - Supports OpenID well. Other than a small bug with the way that livejournal implicitly translates http://gnu_lorien.livejournal.com to http://gnu-lorien.livejournal.com,
Con - No text messaging support. This is where Twitter became a wonderful application for me. It's a microblog as often as it's an SMS multiplexer.
I'll let you know as my opinions evolve.