@Simon - I routinely ride 4 hours and more after sunset as part of a long weekend ride and never have to think about battery life. Not having to worry about whether I will have enough juice left for the headlight to last until sunrise when I'm somewhere on a mountain in Nagano during a 600 km brevet is liberating. Descending at night with a dynamo light is essentially no different from descending by car or motorbike because you can always see where you're going. With battery lights one tends to have to chose between adequate brightness and adequate battery life.
I have SP Dynamo Hubs on both my Bike Friday and my Elephant NFE. So far I've had absolutely no problems on either of them. Between them I've logged about 15,000 km, roughly half as much as I had put on the Shimano DH-3N80 on the Bike Friday before I made the switch to disk brakes and had a new wheel built for that. The SP is slightly more efficient as well as lighter than the Shimano, but also a bit pricier.
I've had very good experiences with B&M Lumotec lights. On the Bike Friday I use the IQ Cyo N plus. I use it with a battery operated rear light. On the NFE I use the B&M Lumotec IQ Cyo Premium senso plus as a headlight and the B&M Lumotec Secula Plus as a rear light.
In practice the Bike Friday headlight is somewhat brighter than the NFE headlight even though the NFE headlight is rated with more lumen, but that's probably mostly a function of the smaller wheel = 33% higher RPMs on the Bike Friday that helps with power output at low speeds.
Both have been totally reliable. I've never had any issues with contacts or humidity, even though I ride in any weather. The Shimano standard connectors used by both the DH-3N80 and the SP have no issues with moisture or corrosion.
Both the Shimano and the SP have no noticeable resistance when operating. By that I mean that I can't tell from how hard I pedal whether the light is on or off, I really have to look. When you spin the wheel manually, the poles of the magnet make for a noticeable pulsating resistance pattern, but that alternating attraction and repulsion evens out with momentum when you coast, it does not show as friction.
On the Bike Friday I went for Cateye Rapid 3 – TL-LD630-R rear lights with Eneloop rechargeable NiMH cells, simply because I couldn't make up my mind what dynamo rear light to go for. These work well enough. I change the NiMH cells for a freshly charged pair about once a month, since rear lights (especially in blink mode) draw very little power, unlike headlights.
For the NFE I went for a dynamo rear light. There are two versions of the Lumotec Secula Plus, one for mounting on the fender and one for mounting on a seat stay, seat post, etc. Since my NFE will always be running with fenders I went for that version, but for a lot of people the other version will be simpler to use (e.g. when using a rinko bag).