I have been following CEC advancements with some interest, but so far support for the protocol among a/v devices seems to be sporadic and quite fragmented. Everyone uses their own "standard" and few devices support it at all. With this in mind, I have not yet purchased any hardware to interface with it, and i doubt anyone else has either. I would love to see it supported though, and its good that there are now affordable interfaces. The most likely present themselves to the system as a RS232 port too, which means someone could get started with a Generic Serial Device.
It seems that most manufacturers use it to control other a/v gear from a TV, though with LMCE we want to control the TV (and other a/v gear) from LMCE.