I'd suggest that this thread be resuurected with comments from those of us running Alfine hubs.
Mine is about 3 months old now and underwent a dramatic "stiffening up" as the bad weather peaked and has not really lossened up. I suspect that the roller clutches have become contaminated.
Everything works well and there seems to be no particular loss of pedalling efficiency, however, there is distinct resistance to freewheeling - personally, coming from fixed, this feels fine since I rarely stop pedalling. However, I clearly need to strip and oil bath the hub.
I have changed the sprocket on mine. The 21 tooth fitted did not come with a "chain guard" and I lost the chain a few times as a result of it either riding off at the front or back. Running the chain very tight made the transmission feel terrible. In any case the hub crept forwards slightly of its own accord and then the chain would come off a few rides later.
Since I found the hub undergeared from stock, I replaced the 21t with an 18t cog which comes with a "chain guard". I took a link out of the chain, put everything back together and despite the chain looking pretty slack, everything runs very smoothly.
I now feel (possibly due to winter tyres) that the hub is a bit overgeared. If changing back to slicks doesn't solve this, I may fit a 19t cog.
Overall the hub is really easy to live with. Wheel changes are easy, removing the wheel is straightforward, although a headlamp would help for night time visitations "in the wilds", and the range of gears seems usable.
I recently serviced a bike fitted with a SRAM Spectro P5. This required so much dissassembly of fiddly parts to remove the rear wheel that I would judge in the field repairs as pretty much impossible without a strong likelihood of losing something vital. There are 3 parts to the gear change mechanism that end up as loose parts on the floor!