I have a Nexus 8 on my Dahon, and a friend of mine has an Alfine 8, I don't really notice the losses on my bike but do on hers, completely different bikes though, mine has 20" wheels and hers 26" wheels.
The Alfine is smoother on gear-changes, but again that could just be the shifter, grip shift on my Nexus and levers on hers.
A bit heavier on the rear too, but so far we're both very pleased with them.
There are a couple of bikes out now with the new Bosch crank drive and an Alfine 11sp hub that I have my eye on
