I always key my audio upgrades to major changes in Dolby's consumer home theater offerings. It generally takes them five to seven years to make a real (as apposed to marketing) change to their stuff, so that tends to define my hi-fi upgrade horizon. AC-3 has been "it" since... 1999? 1998? And affordable (to me) since 2002. Sure enough, a new Dolby standard has been defined, right on schedule. If I'm reading it right, they're going to have trouble upgrading this one. Seems it provides soundtracks with the exact same fidelity that the studios use on their theatrical releases.
We are planning a major upgrade of the visual bits of our home theater this Christmas. However, the format wars between blu-ray and HD DVD still seem to be raging, and prices are still quite high. I think we'll get the best damned TV available in our size range (46"), and then wait at least a year or two for things to settle out before starting the next round.
Besides, I only got my high-zoot receiver a year ago. It definitely hasn't run through its depreciation yet.
But it is nice to know there's an upgrade path out there. And those of you who were looking to do an audio upgrade this year? Well, it may well be worth it to hold out until the new stuff is available. It will definitely be worth it.