Looks like my Ultegra cassette is history. The chain (newly installed, proper length) skips when hammering on the smaller cogs. On my training ride this morning I stopped at some bike shop. A quick look by the shop owner and the diagnosis was there: worn cogs, also the larger ones (on which the chain did not--yet--skip).
The cassette lasted some 11,200 km (6,960 m). I have ridden also in pretty dreadful weather, but regularly took care of the drive train. Maybe should have replaced the chain earlier?
The shop owner said that my problem is common. His advice is to replace cassettes every 10,000 km (6,214 m) and chains every 5,000 km (3,106 m). I wanted the cassette to last two seasons, not one. Am I expecting too much; should I just accept and spend the bloody money?
Does a short life span like this seem feasible to you people? I realise that it is hard to come up with some standard mileage which should be in a new cassette, with so many varying factors at hand. But I would appreciate getting an indication.