never used it as i have never and will never own a bb handset, but from what ive heard BBM has real advantages over whatsapp, but they are mostly for corporate sectors. i mean i cant see why consumers would need centrally managed groups or distribution groups. i could be wrong as like i said ive never used it, but i guess the majority of whatsapp users have never used it either.
i will give it a try if it ever makes it out the stable for android as a curiosity but as per whatsapp will only use it if demanded to by a friend.
On a side note, since i couldnt replace my nokia n95 with another nokia and was forced to go touchscreen keyboard, i hate texting. a phone call is so much easier and quicker for me. i find the whole thing a bit insane, i have standard sms for talking with my parents, whatsapp for one group of friend and gtalk for another . ridiculous.