qooxdoo is made by germans and this is also how it 'feels':
- serious engineering work
- powerfull
- solid
- rather heavyweighted
- rather complex
so this is not a toy, just have a look at the real-life list:
http://qooxdoo.org/community/real_life_examples
So I'd say:
* QOOXDOO -- serious, enterprise windows-like desktop apps
* CAPPUCCINO -- stylish, graphic-centric, mac-like apps
(And it's not really that much easier getting graphics-intensive stuff done in Cappuccino, compared to something like Raphaël.)
Cappuccino just looks better by default. It shares this advantage with ext.js, compared to the e.g. Dijit (and qooxdoo). Whether that's actually worth that much is a good question, considering that any respectable outward-facing webapp is bound to have a style of their own and plenty of designers to make that happen. In that regard, I thin Cappuccino might be even more suited to intranet enterprise applications, where there's not that many designers around and having a default good look is definitely worth it (and having things look like a desktop app is actually an advantage).
In the end, the big difference is between the desktop way of doing things the more common jquery/dojo/YUI enhanced-web page style.