For information on currently available hubs see the Cyclo-Pedia HPV catalog. In fact, why don't I just copy the description since I have it handy. When done right, this results in a compact, well balanced, good handling machine. One option that some are looking to are the geared hubs. These are not without their problems- they will not accept freewheels, internal gear ratios are fixed, heavy etc.
Installation is usually very easy.
We also carry a large selection of repair and replacement parts. We can also build any of the SA hubs into your rim or ours. This is nice from the maintenance standpoint since you don't have a deraileur there to get mud thrown at it from the rear wheel. There are other drive systems in development. This reportedly gives infinite adjustment between ratios from 1 to 4.5 and works with two cables and can spin on to conventional freewheel threads.