Contextual filter in Views for taxonomy browsing
Since that moment I have messed with my views to a fubar state. But looks like I pinpont the rule of thumb that I haven't heard anywhere: when you set up a context filter, eg. for "Content: nid", you don't add it to the regular filter list on the left hand side. And you don't have to bother with %-style placeholders.
At any rate, thanks JoeS for your readiness to help. I bet you will have a bunch of chances to help me out, as I seem to attract all kind of Drupal surprises ;-)