I'm going to re-introduce myself as a clueless newbie.

Just like my audio collection, I like to waste vast amounts of hard-drive space on keeping digital copies of my very small DVD collection for easy playing & safe-keeping.

I have heard about HuffYUV as a competent lossless video compressor, but as far as I can tell it only works on mpeg files? I would have to extract the m2v stream from my VOB files and then compress those.

From this compressed m2v, would it be possible to easily recreate the VOB again for an identical backup, with any extra features or subtitles intact?

Could any answers be pitched at a nice low level please, I seem to become incredibly slow on the ball when it comes to video concepts

The huffy version will losslessly represent the video information from the m2v, but it will be significantly larger than the m2v version, and it won't be possible to losslessly recreate the original m2v (or VOB) from the huffy version. Just create a copy of the source data (VOBs) if you want to make a backup

Forgive me for asking, but why would huffYUV make the m2v larger? Because DVD's are just high-bitrate MPEGs, so it would be somewhat like feeding a 500kb ogg into FLAC and expecting something smaller?

Mac: Correct - The MPEG2 would need to be decompressed to get into HuffYUV.

I want DVD's to come in lossless, each film taking up 20 discs

Best to stick with the mpeg2 for what you're trying to do. It's already a lossy compression. Also, with HuffYUV you're talking about ~10meg/second. The most elegant solution would be: get a biiiig drive, rip the discs to ISOs with DVDdecrypter, mount the movie of choice with daemon tools, and recline with a bag of popcorn. Or just suffer with mpeg4 like the rest of us.

We may have uncompressed DVDs if those Blu-ray discs catch on. Or would we rather put 20 compressed DVDs on one disk? Decisions, decisions...

HuffyUV wouldn't be the best choice anyway. It is only capable of YUY2 and RGB24/32. A YV12 codec such as VBLE or FFV1 would make more sense. Although in the end, just as pointless.

They are not that large, only ~50 GB. Besides, I would prefer a compressed HDTV picture (1920x1080)...

Good Grief! You are going to store DVD resolution into uncompressed YUV format?
Have you ever done any calculations on the storage requirements?

By the way, I know that HDTV is based on MPEG2 but did HDTV requirements increased the frame rates for better temporal resolutions?

I think 60 frames progressive are possible, but only for 1280x720. Only 24p, 30p, 60i are allowed for 1920x1080.