>BBM has statuses for delivered (the message has arrived on the recipients device) and read (they have actually opened it). It's very very useful.
BBM will tell you if a message was delivered successfully, but it's also capable of telling you if a message was read. The catch of course is that the user can control whether or not they want people to see if they've read the message. Ditto for iMessage.
When it comes to iMessage, I wish people would turn read receipts on. The default is off, so most people don't bother turning it on, which almost makes the feature useless.
I'm glad it's off by default - I think furyg3's post above does a perfect job of explaining why.
I'd also add another issue that makes them bothersome - lots of times I read short messages via their incoming notifications which (afaik) doesn't update "read" status. So if I had read receipts on, I'd often appear to have not read something for hours that I actually had.
Not that these issues make read receipts for short messages useless and I suppose it's nice to have them as a feature for groups of people that want/need it for whatever reason, but I think opt-in is the right default for it.
BBM will tell you if a message was delivered successfully, but it's also capable of telling you if a message was read. The catch of course is that the user can control whether or not they want people to see if they've read the message. Ditto for iMessage.