If you've not managed your system so that logfiles don't exist, that isn't the problem of the "hidden volume" system
Oh, no argument there at all. Most people will simply say "It's in a hidden volume, I'm safe! ROFL" and ignore the fact that various other things happily log what they've been doing, leading to evidence of said hidden volume.
And never mind logs, if one has a 100mb TrueCrypt file, but the mounted volume only reveals 1k of space...one's going to have some more questions to answer.
Note : I'm reading what your saying as "the files containing visible and hidden TrueCrypt (or something else) volumes AND ONLY THOSE FILES AND NOTHING ELSE WHATSOEVER" have been cracked by the spooks and the results described in public in formal court proceedings".
Yeah, pretty much. The case I was thinking of is rather old now (and I can only find a couple of [dodgy] links to it): http://webcache.googleusercontent.com/search?q=cache:CvUs7ezVExQJ:myreader.co.uk/msg/1303199419.aspx+&cd=1&hl=en&ct=clnk
Was it a "simple" brute force of a short password? Probably, the actual technical details of what went on are unknown to me. I wish I could find a better link that that one.
Which brings us back to earlier points. Simply using TrueCrypt (and others like it) is not enough, they need to be used properly.