I spent about a week downloading perhaps 7 CDs for Woody (I guess it would have been 2002). I'm fairly sure I never actually installed packages from most of the CDs.
IIRC most of the x86 packages were on disc 1 and 3. I don't think I've ever touched the rest.
People can elect to install a package called "popularity-contest", which reports what packages you've installed to a central server. At release, the most popular packages are put on the first discs.
Each set of discs is for one architecture only.
I downloaded all 7 CDs for Woody, but didn't actually know how to burn a CD from an ISO, so I ended up with 7 coasters. I figured out my mistake and tried again the next week, but this time I picked a distro that only needed one CD: Ubuntu (Hoary). Never managed to get back to straight Debian since then.
When I first installed Woody, I didn't know that you could "apt-get" from the net. I don't remember ever using any of the CDs but 1, but I still have all seven for nostalgic purposes :3