I recently set up two bikes with Shimano dynamo hubs and
Luxos U lights.
I built the
DH-3N80 into a 650b rim for my Rivendell, and I bought a
pre-built wheelset with the
DH-T780 for my KOM.
They're both great.
The T780 rolls really easily, with almost no perceptible drag with the light off.
I can feel a little drag on the 3N80, but I've gotten used to it.
According to testing and reviews, Shimano hubs are a little heavier and have a little more drag than SP or SON hubs. I went with the shimano hubs anyway since they were the cheapest.