What's more important in a social messenger?

If you have a second, would be great if you could tell me which features are most important in your social messenger (bluepulse, twitter, pownce, jaiku, mig33, etc.) Go ahead and choose as many as you like, and please comment on the post if you'd like to say more about your choices or tell me what's missing from the list. Thanks!

What's more important feature in a social messenger?
	All my friends are on there already
	Works great on my mobile phone
	Quick to update my status
	Publishes RSS feed of my stuff
	Good privacy and spam controls
pollcode.com free polls

(This is part of Shai Coggin's 52 Weeks of Blogging Community project.)