Maintainence free isn't completely correct as Shimano IGH hubs do need regular servicing and this is especially important after a break in period as all those new parts will mate with each other and in the process leave a lot of tiny metal bits suspended in the grease.

If this is done you can expect a much longer life from the hub and after that a service interval of 1 to 2 years is suggested depending on use and riding conditions.

The Nexus series is not nearly as a good as the Alfine 8 speed and they have been known to fail at 10,000 miles if they do not see regular service and believe this has been updated in Shimano's technical documents.

I get this information from a shop that specializes in internally geared bikes and does a great amount of servicing on them.

Servicing them is not that difficult as unlike an old SA 3 speed hub the new IGH hubs are modular and come apart fairly easily.

Internal gear hubs are still the bomb and an excellent choice for urban cyclists... the Alfine is showing itself to be durable enough for off road and touring duties as well.