After spending a few more hours exploring the gamma correction issues on mac and pc, I decided to check out how Apple handles the problem. The following three captures were taken from the Fantastic Four trailer, encoded by Apple's own h.264 gurus and advertised prominently on their Quicktime website.
Here is the clip as seen on a Mac running the latest version of Quicktime player:
Now, here's the exact same clip, as seen on Quicktime for Windows:
And, just to make things more complicated, here's the same clip as seen on VLC (a 3rd party player) in Windows XP:
As you can see, Apple obviously super-saturates their source material so that it doesn't look too "washed-out" when viewed on PCs. The result is that the colors also look extremely vivid on Quicktime for OS X. VLC has a much better rendering engine than the Windows version of Quicktime, and so the color correction is more accurate.
But what does this all mean? Unfortunately, compressor doesn't have a simple "saturate" filter. So, for the Fein videos, I had to explore around until I found a combination of filters that produced an image that looked decent on both Macs and PCs. Although it's far from a perfect solution, I think I've arrived at a template that will work reasonably well for now. I color corrected the highlights and midtones on the source by a factor of 18, and increased the gamma to 1.3. This produces an image that looks slightly too saturated on a Mac monitor, but not too washed-out on a PC. This compromise also seems to work reasonably well for digital projectors.
However, it should be noted that the Fein files were originally captured and encoded on a PC. For material captured and encoded on a Mac, no gamma correction should really be necessary (at least in theory). PCs capture analog images with a gamma of about 0.45, and display them with a gamma of about 2.2. Macs, on the other hand, encode at 0.55 and decode at 1.8, which is far more accurate (and which is also, incidentally, why image professionals and CGI studios like Pixar tend overwhelmingly to use Macs instead of PCs). So, in other words, video captured and encoded in Mac OS X is higher-fidelity and far more cross-platform compatible than video captured and/or encoded on a Windows machine.
My recommendation? We should be capturing and encoding everything on Macs. Ideally, material would be captured from a clean source (i.e. DVD) through S-Video (or firewire), encoded in a lossless DV format (such as Motion JPEG or one of the Final Cut Pro codecs), and then transcoded into high-resolution h.264 at something between 800 and 1500kbps.