Well if you think of iMessage as equivalent to texting then it is pointless. But that is not the fault of iMessage. As for data... it uses so little that it is not even worth mentioning. If you sent 1,000 160 character messages per day that would only be 5MB of data in an entire month. It doesn't even make a dent in even the smallest data plan. So I have to shake my head at the data concerns.Message for me is pointless. I have unlimited text and so do most people I know. I also have unlimited data so it's not a big deal but most people I know do not have unlimited data so they have turned iMessage off so it doesn't eat up their data plan.
And I have no need to text to iPods. That's a high school/middle school kid thing.
As for me, I would much rather use iMessage than plain old text. With text I don't even know if the message was actually delivered, let alone read. In a back and forth conversation with iMessage I can see when the other party is in the midst of typing so I will often wait to see what they are typing before sending another message. With text I would have sent a message that might not even apply. Then the back and forth crap to correct it. Let me not forget the classic "sent my text just as I got yours."
Anyone who is already using IM should feel right at home with iMessage (ditto for BBM users). Regarding the people I know on iOS 5.x , we pretty much have all stopped using whatever flavor IM each of us preferred. No longer do I have to remember that Tommy uses Yahoo and Rosalie MSN Messenger. Now it is just iMessage. Better yet if either of us have no access to data but still have cell signal for voice, iMessage will automatically send as text. So that tops just about any IM app in that regard.