I've covered ~13,000 miles on my Alfine 8, using it as my daily commuter. It's been extremely reliable and, aside from one shifting problem that was traced to a fault in the shifter, it's been no problem.
It was mentioned up thread that this needs a service every year/3,000 km but I've not found that necessary. While trying to identify the shifting problem, I was worried that it might be because I'd gone 10,000 miles without touching the hub, or even the gear cable adjustment, so I scoured YouTube for all I could find about checking and servicing the hub. There were all sorts of scare stories and talk of specialist Shimano service kits at nearly £100 (every 2,000 miles?!) so I found one channel where the guy seemed very knowledgeable and had decent videos.
I bought the things I needed and removed the hub and carefully split it open. I was ready for the horror of orange coloured sludge from the reported water ingress problem but was delighted to see that there was absolutely no evidence of this at all. The grease was still beautifully milky white, with everything looking like it had just come off the assembly line. So, despite having got that far and having bought the stuff for doing a lube bath, I decided to leave well alone. If it works, don't fix it!
I like the simplicity of it, not having to regularly fettle with it as I did when using derailleur gears, and that fact that it's all enclosed. Which reminds me, I must see if I can find a chain enclosure to get even more life out of my chain.
My reason for choosing Alfine-equipped bike was a compromise between reliability and cost. I couldn't afford a Rohloff and the reviews of the Nexus were off-putting.