I like bikes with gear hubs and currently have three. These are a Duracycle fixed gear frame with a older SRAM 3 speed hub, a Swobo Dixon with a SRAM iMotion9 and a Civia Hyland Rohloff.
From the above you can see that I like European gear hubs. The primary reason is that the manufacturers have a lot more technical information available for them than Shimano or Sunrace Sturmey Archer. Both the owner's manual and downloadable SRAM technical manual covering their gear hubs provide much more information on specifications, installlation and maintenance. The Rohloff English language manual is 132 pages and covers everything regarding installation, use, maintenance and repairs.
The information provided by the far eastern manufacturers is minimal in comparison.
One example is minimum input ratios. SRAM, Nuvinci and Rohloff all provide clear minimum input ratio information, ie: minimum size ratio between chain ring and hub input sprocket. This limits the amount of torque the hub is subjected to. Rohloff and Nuvinci also list actual maximum input torque specifications.
The far eastern hub manufacturers do not publish such info, or at least it is not clearly stated. Based on the numbers I got from their technical support they allow much lower input ratios but, based on posts I have seen several places, it seems that strong riders can abuse them beyond their strength limits at the allowed input ratios or higher.
Are the Shimano hubs stronger than SRAM units? Based on the input limit of a 33 tooth chainring and 23 tooth input sprocket Shimano allows it would appear so, but in the recent shaft drive bike thread posted here a 235 pound user reported quickly destroying two 8 speed Shimano hubs so far. Rohloff is adamant about minimum input ratios and lists two, one for riders under 100 Kg and the other for heavier riders and Tandem use.
To me the advantages of the gear hub are ability to shift while moving or stopped, extended chain and sprocket life and reduced maintenance. Disadvantages appear to be that many bike shops do not want to service them and they can be heavier than an equivalent derailleur gear train. I am not making any claims regarding reliability. good or bad, as this seems to be highly dependent on the input torque level the unit is subjected to for many of them.
I am interested in hearing from other members regarding their experiences with gear hubs, good and bad. This includes units of any make and age.
BTW there is now a Yahoo group primarily dedicated to gear hubs and geared hub bikes. For those interested here is a link.