This. I started to get involved in Debian a few years ago (though I'm a long-time user) and this is really really interesting work. There are a lot of packages with too little workforce where you can go through a list of dozens or hundreds of bugs.

alrs is true ; in most cases your work is automatically replicated to Ubuntu (where the package-maintainer relationship is less strong than in Debian. Most packages don't have a dedicated maintainer there).

And everyone can do it ; no sign-up or complicated process required. You just have to find a sponsor for your packages which is just a fancy name for "every code needs review". Debian is often described as bureaucratic but most of the processes are very sane.

Well, wherever the help is needed. My point is that if we can get a large number of skilled developers involved in improving the code behind Ubuntu through a small weekly commitment, that could really solve a lot of the existing issues.