There are a large number of ways to contribute to 'Linux and open source'.
If Canonical continues with things like http://design.canonical.com/ then that is a huge boom for Linux desktop efforts in general. Even if they do not contribute a lot of code back upstream, simply taking the code they can get and making it perform correctly and be friendly will show Gnome developers in what directions they should proceed. It's one thing to just blindly write software that you think will provide benefits to people... it's quite another writing software you _know_ will provide benefits.
Even if Canonical does not produce a single line of code back to upstream their efforts have contributed far more for the Linux/Open source desktop efforts, specifically, then any other distribution I can think of. Just having something friendly for non-technical people is valuable in it's own right and after using a number of different distributions over the years I can say that Ubuntu has gone the farthest in user-friendliness then any other distribution despite it's technical deficiencies and numerous mistakes they've made.
> I still think RH has the best and most sustainable FOSS business model so far, hell
Yes. Proof is in the pudding, (when profits == pudding) Making money and finding a way to be valuable to many different organizations is a huge huge win for Linux. Redhat's contributions back to OSS is probably the most valuable any corporation has done to date (in general). Fantastic company.
> I might even switch back to Fedora if their update madness can be tamed (e.g. not include brand new stuff like SystemD etc.)
Funny. I was thinking of switching to Fedora specifically because of things like systemd. :)