One of our Alpha Testers, Joe Rice of GMX Entertainment, posted the following great summary on the DVD List on 06.25.07
BD has supported recordable and re-writable media from the get-go, and those media tend to be very compatible at a physical level with BD players. Drives and media are easy to get, with a number of brands available for each. The logical side of things is a bit more complex and frustrating, however....
As background, BD supports a couple of audio/video modes, BDAV and BDMV.
Consumer-oriented, and offers basic A/V playback, chapters, and simple menus (I think - haven't looked at it much). Any player which supports BD-R/BD-RE playback should support BDAV playback.
What's typically thought of as BD, with full HDMV and BD-J support. This is probably what you're looking for. BDMV on BD-RE was spottily supported initially, but most players have caught up. This combination has been officially sanctioned by the BDA with BD-RE 3.0. The main difference between BDMV for BD-ROM and BDMV for BD-RE 3.0 is in AACS encryption settings. I believe that at this point, any player supporting BD-RE playback must support BD-RE 3.0.
Player support for BDMV on BD-R/BD-RE was a bit slow in coming, however most players now support it. In some cases firmware updates are required, so make sure the most recent updates have been applied. ( They happen frequently - for instance, Sony posted updates in the last two weeks for the BDP-S1 and PS3, and Panasonic posted one yesterday for the DMP-BD10). Some specific notes:
HD DVD specified recordable/rewritable media some time ago. That said, while media is available, standalone drives don't seem to exist in the market. I've heard of some Toshiba computers including them, but have had no success tracking down a drive for purchase. I'd love for someone from Toshiba or Microsoft to prove me wrong on this, as we could use one!
Until drives are available, QC of HD DVD needs to happen either in software players, in a Toshiba emulator, or using DVD-R/DVD+R DL/DVD-R DL in a retail player. That means that to check in an actual player, you have less than 1/3 of the capacity of the final disc when testing burns. This means extra time spent in making special cutdown builds to check various pieces of nav and linear QC, and no way to check the full disc.