Short note: My laptop's new USB sound card made annoying crackling noises at high CPU load (simple check: swipe mouse over buttons in task bar with full plasma desktop effects :-) ) . Apparently this is due to the USB bus not supplying enough power, because I got rid of this by using an externally powered hub.
Hm. Simple solution, but dire consequences: lugging around a fat hub and its power supply? Or get a Y adaptor (like this one) and let it block two of my precious USB ports? Not amused.