In addition to what paulkoan said, plugging your N900 in to a windows computer can still be damaging. There are more than a handful of viruses floating around that will embed themselves in near on any file if there is the potential to do harm. Think word documents, file name changes, icon changes - it's a very long list.

Your data can still get hosed by viruses, Maemo wont much care or even notice this, which is nice, but it can still be a double edged sword.