Yeah, that's the problem with compression. In the DOS 5 days, me and my 386 spent many a night cruching away to compress that 40 meg drive into a 60. Or maybe a 70. 2:1? Never. Oh sure, you could set the estimate so it'd say 80 to start with, but you'd never get that much on there.
And this was in the pre-mp3 days obviously. I didn't have many jpgs, etc compressed files either, just windows, a couple games, my Lotus suite. 1:3 was the ratio I actually ended up at usually in those days. Even if compression's more efficient, the files are already compressed like X said so it's a lot of work for very minimal space gain.
Plus, at least this is how it used to be, the compression would take the entire HD and cram it into 1 huge file, the volume archive. So if even one block on the HD went bad the whole thing was easily lost. Not good.
Good idea to leave it as a fond memory of the 200mb HD days
--Mc