A few weeks ago the headlights on my 98 S70 started going out intermittently while driving. The next morning I noticed that jiggling the switch while in the on position made the lights flicker. Replacement at the dealer cost about $100 (about $60 for the part). The service guy at the dealer commented that switch failures aren't all that unusual. My car had <65k mi at the time.

I would try playing with the switch while watching the lights to see if that is the problem.

I also recommend getting this fixed soon. I was really uncomfortable driving the family home the night I started losing my headlights!