W/a 40 mi rt daily commute I use my singlespeed conversion w/my loaded commuter. M&F I use the multi-geared commuter to carry a week's worth of work clothes and food. T-Th I ride my singlespeed w/a fanny pack(yeah a fanny pack...ya gotta problem w'it?) for essentials. Glasses, keys, wallet, etc. I like the speed and simplicity. The gearing is 46x16 w/no wb cage and my pump, patch kit, tools, etc. are in an mtb frame bag though it's a road bike. It works. When climbing a hill the other day I suddenly 'got' how having a fixed gear would make climbing slightly easier. But, overspinning or holding back on the decends would be murder. The 'powerband expansion' and coolness aspects of riding a fg or ss are secondary, but there nonetheless.
I'm a stronger rider now that I've been riding a singlespeed for a couple of months w/consistancy.