Ok, here are some news:
1. I got it to compile for the N900, and
2. I got it running on my N900
3. I modified the UI slightly, to make it fit the N900 screen. It is still a bit tiny, but it seems usable
4. It doesn't seem to synchronize the folders recursively. I don't know if it is a bug or a feature ?...

If you want to try, I have attached the .deb package made by QtCreator. I'll try to take some screenshots, too.
To start the program, launch it from terminal with this command:
/opt/owncloud_sync/bin/owncloud_sync_qt

But be aware that the program doesn't close by itself, as it thinks there is a systray. So you'll have to kill it by hand, using htop for example.

It is a very early package ! It doesn't do awful stuff, but it may crash.