I tried the AppUp Center. It operates somewhat like the AppStore in iTunes in that it shows you available applications, some free, some not, and lets you install them. The introductory text talks about trials, but I didn't spot any. You can leave reviews.
In order to download anything, even free, you have to sign up for an account and give a credit card number - again, like the iTunes store.
I didn't immediately spot anything that looked enticing, so I tried Boxee. Yes, you can download Boxee directly but what the hey. It downloaded and installed, but would not launch. Not sure what's going on there. Of course, the idea of running Boxee on the Mini 9, or most current netbooks for that matter, is laughable.
It's annoying that you can't even see what products are in the store without installing the software - the web site is very sparse. It is "beta", though, and brand new. Give it time.