Bike Quarterly did a pretty thorough comparison of generator hub resistance so if you want numbers to back up the anecdotes, check it out.

Basically with an average speed of ~18 mph, with one light switched on, the Shimano 3N71 takes off maybe 8 watts of power from your pedal stroke because of drag. The Schmidt is a little more than 6. With the lights switched off, a Schmidt adds only 1 watt of drag, and the Shimano adds 2. So, in real terms, it's not a lot of difference between the two, but your mind can excacerbate the differenece if you're tired and cranky, so perhaps it's worthwhile to spend money to know that you've bought the best.

I have a Schmidt dynohub on my brevet/commuter bike and have never regretted it.