To clarify a couple of things:

1. I run the Ubuntu One app developer programme, and I've newly got an N9, so I'm really interested in having both Ubuntu One files and Ubuntu One music streaming working on my phone
2. I'm currently looking at building U1 apps with PhoneGap, because I'm best with JavaScript stuff; if someone were interested in building an N9-specific app with C++ and Qt and so on then I'll happily give pointers to the APIs to use and how to do it, but I won't be much help with the actual code
3. There is currently no finished PhoneGap port for N9. but I know bundyo's been working on one, and I'd like to try and get that running, so anyone with pointers to how best to do that will be gratefully listened to (I'm new to Meego stuff, so I don't really know what I'm doing with Qt creator)
4. I've got a mostly working version of Ubuntu One files in Launchpad at lp:~sil/+junk/u1files-html/ -- it allows you to browse files but doesn't yet let you download a file to your local device. It will work in Chromium (which is the only desktop browser which supports the necessary APIs, right now), if you start Chromium with the options in start.sh (and you'll have to quit Chromium if it's already running)
5. I'd love help with this. I'm happy to talk about the way it's meant to work, or to give anyone wanting to work with Ubuntu One on Meego any pointers they want; just ask away!