Very nice indeed. There's only one thing I havn't figured out: I've put two archives on my N900 (Dutch and English). But I only can seem to use the English Wikipedia. Is it possible to switch between two archives? Or use both of them at the same time? Thanks!

There should be a button next to the search bar, where you can switch the language. Furthermore, when you view an article in the browser, there is also such a button at the top right (you will be redirected to the online version if you choose a languages that is not installed).