Hi Pieter,
This almost a short story, and it is hard to get te point. If you want more web 2.0 get some nice javascript from internet or write your own and put it into a Mendix widget. And of course, like we all do, share it with us :-).
If you want to extend your app, it's up to you. You are not the first one building a file sharing site, so look around for bright ideas. But be careful Mendix is not a native CMS.
At last there should be something like business processing in it, e.g. workflow (somebody reviewing your documents). Just store and share can be done in all platforms and languages.
Hi Chris, Thanks for your honest comments. I am sure nice applications can be made using some of the above standard components to create new community like websites. "It is indeed only the imagination of the developers, as you have mentioned." Maybe this short component list helps people to get ideas for developing great WEB 2.0 Apps and kickstart into Mendix. :) I will post some projects or idea's hopefully later on.