Here’s some info on Combustion 3 from Videography Magazine:
"combustion 3 is the first effects application to have integrated editing. By doing this we’re not trying to replace something like, for example, an Avid system for long-form editing. However, there are a lot of times when you’re working on something like an opening, a web banner, or a music video, and you need to string clips together with transitions. Traditionally, users have to go out to an NLE to do that kind of work. And that’s complicating their workflow in a couple of ways. First they have to find the NLE and learn it. Second, they are always changing things around. What I mean by that is, there’s a sequence of clips that looked right for what you were doing, but after you make changes, the timing might then be off or you didn’t get permission for the one clip you were going to use so you have to swap it out. By doing this all within combustion, you are saving a lot of time are also finding the process considerable easier. I showed it at Siggraph to a number of our large postproduction customers and they thought it was great. One reason is because the animators hate having to go out and book time in an editing suite with and editor when they just need to clip stuff together. So now they can do all that work themselves."
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Another feature set added to the application, also based on user requests, is the Expressions. As it was explained by Worthington, by using a piece of JavaScript, the artist can control any parameter in combustion that’s keyframeable. “And that’s almost everything in the application.” he says.
Editing and Expressions, sounds like a good upgrade to me, the article also talks about it running on the G5, so I think that should dispel the rumor that it won’t run on OS X.