What's the steepest hill you can tackle on your single-speed? I'm (still) working on a design for a SS folding commuter bike, so have been riding my Rockhopper, with road tyres, in one gear to work and back. It's about 6 miles each way, fairly hilly and have been doing it for about 6 months.
I've found that any crank speed that allows decent progress on the flat or down hills causes me to slow to a painful walking pace on anything much steeper than about 1 in 10. I've come up with a ratio that I think gives the best of both worlds (i've forgotten exactly what that is, will post it later) but I still have to freewheel down most hills and accept a lower speed on the flat.
A road, when tackled near the end of my commute is about 1 in 6 and I almost have to get off and push. How often do you other guys get off and push? or do you just avoid steeper inclines?
I am a convert to singles though. It is reassuring knowing what to expect every time you pull away from lights and not have to arse about with changing gear needlessly through dozens of speeds. I also think it allows your body to become used to employing one spread of effort/torque