It was a mix of both - the Ubuntu 6.04 was in fact one of the freely distributed pressed ones, but many were home burned CD-Rs - photos, software, data backups, etc.
Burning tens of DVDs is a little tiresome, but it is well enough scripted that it is easy to slowly swap them in and out while focusing on another task - the brief interruption is barely noticed.
It also means that the failure of a whole disk has a lesser impact on the whole.
Edit: that said, I do have a spindle of 100 CD-R that were given to me. I haven't had the motivation to use them up yet.
Anecdotal evidence, but I've recently gone through my ancient CD collection (in so doing, I found Ubuntu 6.04 installers, AOL dial-up CDs and other relics) and archived them with GNU DDrescue. It had no problem reading all bar a handful of CDs from the mid-to-late 90s and early 00's - the failure rate was much lower than I expected. The failures were mostly completely visually identifiable too - the layers had started to separate.
I've also been backing up personal photos to DVD annually for quite a few years. Each disc contains encrypted Duplicity files, and a PAR2 archive to assist with any deep failures of the on-medium parity. I also usually include a disk or two of pure parity archives, to handle a total failure of any disk or two in the middle.
Each year I check the price of DVD vs. Blu-ray and when factoring in the cost of the burner DVD seems to stay just on top for $/GB. It doesn't help that I've still got spare DVDs lying around, and people basically give away the blanks these days.
This is not my only backup strategy, but it is the only one that is cold, read-only, and offline.