[microtonal]

So, back to Debian, once I want to deploy something and I've played with it on my Ubuntu dev machine, which OS would I evaluate first? Ubuntu Server, of course.

Maybe, but Ubuntu Server has serious downsides when it comes to security updates. Canonical only releases security updates for main/restricted, while Debian releases security updates for the whole distribution. So, if you are using packages from universe/multiverse (which I guess a lot of people do), security updates are not guaranteed. Or as Canonical puts it:

Canonical does not provide a guarantee of regular security updates for software in the universe component, but will provide these where they are made available by the community.

https://help.ubuntu.com/community/Repositories

[rdtsc]

Fair point, thanks for mentioning it.