I've never used BBM on Blackberrys but i believe the best part about it was to be able to see if the other person has read the message that you sent them (ex. you send a person a message when the recipients are driving, and it's good to know they've received your message).

Live Profile is definitely picking up speed in the Android world, my girlfriend just downloaded it on her Nexus S. I'm assuming it's also becoming very popular for iOS.There's without a doubt that this application will be used widely very soon