In my case I don't care for the green/blue bubble divide, EXCEPT that I have a limited SMS plan and every time someone messages me it potentially costs me $0.10. That is not that significant until someone sends a series of short messages that could have been bundled into one, and I can't help but think "this person just cost me the price of a coffee".

It's not even Apple's fault, but rather AT&T's confusing and expensive billing options. I could also upgrade to an unlimited messaging plan, but 90% of the billing cycles I'd be overpaying.