Actually, I was subscribed to the security repository, meaning I only got security updates, and over the year and a half I did this, there were probably no more than 10 megs of updates total IIRC.

You're probably (and the OP, Joey Hess is definitely) talking about Debian unstable, though, which does not have a security repo. (I was on testing IIRC.)

It was not hard to upgrade to a new version of Debian, either, because the tool I was using to download the necessary files, apt-get, would reliably restart the download where it left off, so I downloaded the files over about 7 consecutive nights.

It was pretty sweet, actually. In contrast, I wouldn't have a clue how to keep OS X updated with security patches using a dial-up connection.

Apple's update flow is huge, averaging over a gig a month it seems to me. Probably impractical to download it all over dial-up even if you run the updater every night.

But let me ask why you jumped into this conversation: do you or someone you know of have experience keeping OS X patched over a dial-up connection? Do you have reasons to believe it is possible?