This story at the BBC talks about a recent survey into MMS usage. It's presented in a fairly negative light: the writer concentrates on how little this stuff is getting used, but I actually found it quite positive.
"83% have never sent an MMS
45% do not have compatible mobiles
17% did not know how to send a message
78% of MMS users have sent pictures of friends or family
27% had sent music clips
14% had sent sports clips"
This is fantastic: looking at this survey another way, 17% of the population have used MMS, well over half have mobiles which can handle it today, and 83% know how to send a message.
Given that MMS is a completely new sort of service (try not to look at it as "SMS with pictures", it's positioned, priced and used in a completely different way), and that it requires users to have relatively recently (<2 years old) kit to work, I think this is excellent news.