When looking at the Ubuntu Software Centre I was wondering whether the banner at the top (which contains featured applications) contains paid for advertising, or whether they are just recommendations by Canonical for useful applications?
I haven't seen anything in the app developers section of the Ubuntu website that offers this advertising space for developers.
From what I can see from the software-center specifics, the exhibit banner is just a means to promote a software or a collection of software. The banners doesn't seem to be an advertising space nor do the developers pay to have their software featured there. Simply, the software-center devs are just promoting some of the top-rated software available through the software-center.
Read more about the exhibit banners: