I believe the best feature is that BBM is more secure. It is easier to retrieve messages from Whatsapp, KIK, etc that aren’t meant for you. BBM is also more reliable in the delivery of messages. It will be possible for Android users to share contacts through NFC.
AFAIK, it’s free. However, this may change in the future.
I would say neither. However, it will give them a far bigger user base, which is often equal to money nowadays. There is also talk of spinning off the BBM division from BlackBerry.
It’s a big deal only to their desperate stockholders and die-hard fanboys. They haven’t been relevant in half a decade, just lost a billion dollars, and will likely be bankrupt soon.
Blackberry gives your messages to governments that want it (even before PRISM), so it’s not secure. If you want security, self-signed PGP is a better bet.
If you want read receipts, Facebook does that for free and probably for longer than Blackberry’s remaining life.
That used to be the case. They are in the process of rolling it out to android and iphone this week (was supposed to be yesterday, but it looks like there may have been some issues).