They've blocked me from using their perfectly useable US number for no reason that makes sense to me.
They've provided an alternative to an international number that they claim is costing me more than it has to - but the alternative is another international number, which costs just as much.
All you services: go away. If I'm interested, *I* will friend *you*. If you want to follow my updates, there's a perfectly good RSS feed.
Granted, this last isn't Twitter's fault, but it still makes the service less useful.