HD-100 tape sizes
 

B&H shows the new GY-HD100U as excepting "Standard and Mini DV Cassettes". Does this mean both sizes, or is this a misunderstanding on my part?

It's a misunderstanding on B&H's part. The camera only uses miniDV cassettes.

Yep, MiniDV only
 

But the BR-HD50U will accept both full- and mini-sized tapes. That's really good news because Sony's M10 is Mini only, as is the JVC CU-VH1. Even better is the fact that broadcasters seem willing to accept full-sized HDV as a deliverable. Anything is better than buying more full-sized HDCAM and D5. One other note: JVC sold its tape manufacturing fascility in Korea over a year ago but they must have made some arrangements because during the JVC AVR dealers meeting in Vegas I asserted strongly that JVC come out with a "Super Tape" for HDV just like Sony. "How can I sell people HD100's and then advise them to buy the Sony PHDV tape?" Remarkably they listened and the new tape will ship concurrent with the camcorder and deck. Exactly when that might be is anyone's guess.

Yes, but...

... the incompatibility issue continues.

First, the M10 only accepts mini tapes, which is bad enough. But it also won't record any flavor of 720p HDV, nor will it play back 720p HDV through the firewire port. Also doesn't have any analog component inputs.

Then, the alternative in the JVC lineup is the CU-VH1, which is mini-cassette only. It also cannot play back Sony HDV through the firewire, or record it, which makes it useless for Sony shooters. But it's even further incompatible in that it can't play back or record JVC 720/24p! If you're getting an HD100, you definitely don't want the CU-VH1.

So we can turn to the BR-HD50U, which does take large cassettes as well as small cassettes, can play back DV and DVCAM and can play back and record 720p HDV (including 720/24p). Sounds promising. But... it's still not able to record 1080i HDV, or play it back through the firewire. And no analog component input either. So for those who are shooting with the Sony HDV gear, the BR-HD50U is almost completely useless.

For a JVC-only shooter, it looks pretty well-rounded. For a Sony-only shooter, there is no large-cassette offering available at all. For someone who intends to shoot with and/or do post work with both flavors of HDV, that pretty much means needing to buy two decks.