the 10D .thm files... why, and what can I do?

From my observations, neither Photoshop CS or ThumbsPlus Pro 6 uses the .THM files. Even if deleted, the exif info and previews and thumbnails still work fine in this programs.

Is there any way to disable their creation on the 10D? Or are they required to view RAW's on the camera LCD? I'd just as soon not have them, just wasted space and time, especially when I delete files from Thumbs... it delets the RAW, but not the THM. Very annoying.

Or is this just a symptom of shooting with Canon RAW files?

Quick answer, if you shoot RAW you will also always have an embedded jpeg. Just use the smallest jpeg to get more RAW images on the card.