Did you know that M$ are due to release a revised version of the 360 that will include an HD-DVD drive built in (rather than the current option requiring an external add-on HD-DVD unit) and it will also add an HDMI socket, which is a welcome connection type that many moaned was missing when the 360 was first released.
But I never think that releasing such big revisions in a fixed hardware platform is a good idea. Upgrading the system's media format to one the original revision of the platform cannot run out of the box is definitely not a good move as it could fragment the userbase.
Once 360's start to have an HD-DVD drive as standard games developers are going to want to take advantage of the extra storage space for their games. This will mean that those with existing 360's will need to shell out the £200 for the external HD-DVD drive so they can play games on their older version of the console. Not a good way to encourage people to continue supporting the platform, especially if Sony start to reduce the price of the PS3 this year. There may come a point where existing 360 owners will be able to purchase a PS3 at a price only slightly higher than the 360's external HD-DVD drive, making it an interesting alternative.
Saying that, I've held off buying a 360 due to a couple of reasons. It hasn't largely interested me as a gaming platform due to most of it's key releases also being on the PC and soon the PS3. But the revised version my interest me more. Having HD-DVD playback built in and an HDMI socket will mean it will be a very inexpensive HD-DVD player compared to standalone players. It is also currently one of the best media extenders on the market for anyone using a network primarily made up of Windows XP and Vista based systems, so that in itself makes it of interest to me. Especially as it does do a better job as a media extender than the PS3 currently does, and is better than any of the standalone media extenders I've seen on the market that cost at least half the price of a 360 for just those features alone.