I'm going to vote against this idea for the time being...
Not because I think it's not a good idea, or that it's not the right thing to do, but because distros & or OS choice is like religion to people who care obout such things. To suggest one distro over all others is probably going to wind up being divisive within the Inkscape community and the project as well.
In summary: People will take it personally.
There is also lot of controversy surrounding Ubuntu as a Linux distro, and their dedication to user freedom, vs corporate goals.
However, Doc, I think we ("we", as in you and I) can do plenty to spread the word about Ubuntu as a creative platform, as well as other good/easy to install and use distros, outside the Inkscape project, which would possibly have as much or more sway than a fleeting mention on our website.
It would be cool to approach it from the other direction: Using Ubuntu's popularity as a means of promoting Inkscape, which I doubt would be objectionable to most people in the project.