Hey Gary, (also replying to all in case other SS freaks like us are interested)
I ride almost exclusively single speed, and think it's perfect for this area.
Right now I have a Niner Bikes S.I.R. 9 (Steel Is Real) frame, and I'm running Bontrager Race SS cranks, made by Truvativ and are basically a Truvativ Stylo SS crankset, with a 32t Salsa chainring. In back I'm running an 18t Surly single speed cog. Since I have 29" wheels, 32:18 provides a gear ratio similar to what 32:16 would be on 26" wheels. Rear hub is an American Classic SS.
A few notes about this setup, and your questions below:
- Cranks need to be stiff due to all the mashing you do on climbs - XT cranks are great, as well as the newer Truvativ GXP cranksets.
- Surly SS cogs, and American Classic SS cogs are great because they have a very wide base. BMX cogs are normally very narrow and can chew up your freehub body over time.
- My Niner has an eccentric bottom bracket to handle chain tension, so I have vertical dropouts and discs are no problem. Some other frames go with track style (horizontal) dropouts and BMX-style chain tensioners, which can make running discs difficult because of changing caliper alignment, and difficulty removing the rear wheel trailside because the caliper is often in the way. One answer to this is the "mullet" setup that you mention below, with a disc out front and V in the rear. Vs are much easier to work with when aligning the wheel in a track style dropout.
- Flip flop hubs let you run SS on one side and Fixed Gear on the other. Fixed gear is a blast to ride, but can be pretty dicey until you're more experienced with it, especially off-road. No coasting equals scary downhills unless you have some skills (I don't). This may be why you see front brake only setups, because countering pressure on the cranks serves as the brake in the rear.
I work at Carrollwood Bicycle Emporium and about half of the mtn riders in the shop have converted to SS only or at least have one SS bike in the quiver. We're very well versed on the ins and outs and can always help anyone who's interested in either setting up a new SS ride, or converting an old hardtail just to give it a try.
Have fun with it!