"You must tell me your opinion of MPEG4- will it replace MPEG2? Is it backwards compatible?"
I'm still on the learning curve, I've only really looked at MPEG2 encoding, since that's what we're using. I seem to recall that they're incompatible. Completely different compression which works better, and the streaming protocol is quite different. But I don't know any MPEG4 details (I do remember MPEG2 transmission packets are 188 bytes, and have wondered why).
There are apparently different layers in MPEG4 that can be added together - like a chroma key composition, you can have an English speaking weather announcer to go with the English audio track, and a Spanish announcer with a Spanish track, using the same weather map or satellite image background.
But I'm working on networking stuff at the moment, so it'll be a while before I learn more about MPEG4, I think.