I've got a 5 year old Shimano (3N79, IIRC) and a SON on different bikes. Both used for commuting, the SON has been on a few late-night brevets.
They just work. And with the newer Edelux and IQ lights, there's as much light on the road as I need. The batteries don't run down or die after a few years, everything is permanently attached so I don't have to go rooting in the closet for the charger or mounting clamp in October, but when I get on and ride, the lights do come on. Compared to a fancy helmet light, the road's not washed out (so the bumpiest part of the road can be seen), the trees aren't lit up (but that's not a problem on most roads and streets), and the flashing off reflective signs doesn't drive me nuts with the dyno lights.
They're not quite trouble-free; the connector on the rear light came loose on a brevet, and just last week the connector on the Shimano came loose after I rode over some road destruction -- er, I mean, construction. Not bad for five years' of riding.
If I buy another bike, it'll either come with a dyno or I'll move one over.