A few months ago, I purchased a Sony HDR-HC1 camcorder. (In case you're interested, that's a consumer-level camcorder that shoots HDV onto standard MiniDV tapes. It wasn't cheap, but at 1440 x 1080 pixels, it blows standard DV camcorders away.) Naturally, I did a pretty minimal amount of research before buying this, pretty much limited to Sony's Australian website, and some product reviews, so I was pleasantly surprised to discover that the 'HD' in 'iMovie HD' stands for 'edits HDV footage as shipped'. So, I was editing HDV on my PowerBook from the day I bought the camcorder.
Now, it's not as though I'm a professional film maker, but it's reasonably obvious, once you've put a few hours in, that iMovie HD is a low-end video editing application. So I figured I would fire up Premiere Pro 1.5 on a Wintel box. After patching it to 1.5.1 to enable HDV capture and editing, I started downloading some footage from tape. And that's as far as I got—a 2.5GHz Pentium 4 with 1G of RAM could not even capture the 25Mbit/s HDV stream. There were frames lost and mangled all over the place. Completely unusable.
Let me be clear: a 2.5GHz Pentium 4 is below the minimum specification recommended by Adobe for HDV editing. My question is why? My comparably modest PowerBook G4 can capture and edit HDV without breaking a sweat. What's wrong with Adobe's code such that it can't keep up?