Lots of info on the web about how it burns more calories, makes you fitter etc, but does it allow you to walk faster or further or get up hills with less effort. Well, I have your answer right here. I tried it as I have poles to ease out my knees. Timing myself I would say I could walk faster on a relatively even slope once I got into the swing of it and moving faster does fitten you up. I found using the poles rather annoying though so I tend to keep them for slopes where I need to relieve the pressure on my knees and its a lot slower if you are coming down something really steep such as the devils kitchen in Snowdonia. Also it doesn't really work well if the slope isn't consistent so you keep having to readjust the poles. I do find it helpful when I'm starting to get tired to the point where my leg muscles are aching. So in summary I would say it depends on the type of hill you are walking on, how good your knees and hips aer and the surface on which you are walking ( definitely easier coming down scree or an icy slope in winter. ). I also find it quicker and safer if the wind is getting up to the extent its hard to keep your feet as in the cairngorms.
This video by Nate Goldberg shows just how easily you can Nordic Walk.