The Free Software Foundation has released a statement about the SCO case. In addition to the usual "GNU/Linux" vs "Linux" naming issue, here's something I found interesting:

there remains the simple fact that SCO has for years distributed copies of the kernel, Linux, as part of GNU/Linux free software systems. Those systems were distributed by SCO in full compliance with GPL, and therefore included complete source code. So SCO itself has continuously published, as part of its regular business, the material which it claims includes its trade secrets.

From what I've heard, trademarks, copyrights, patents, etc have to be protected all the time, and not just when the holder of the rights feel like it. So, if SCO has been releasing what it claims to be proprietary code that they own under the GPL, I doubt they could rightfully claim the code to suddenly be proprietary again, just because they decided they needed some cash...