Single speeding is a bit of a crazy at the moment. Certainly a fashion in those big cities I've heard all about.
Or is it a revelation or more a rebirth of a simpler way?
I had 7 Konas...er I mean bikes that happened to be Konas... until I built a '95 Hot up as a single speed just because I had enough bits for SS but not for geared and I wanted to get it out and moving. I had no intention of getting into SS.
What a revalation.
I would not advocate SS'ing your only mtb but if you have a couple SS one of them. You can always convert back!
Remember what riding a bike was like when you were a kid? Yes hills are harder and downhill there is a lot of legs flapping around but Oh Sweet Lord it is just so simple and effortless....like riding a bike for the sake of it. Nothing to think about apart from pottering along.
Don't SS your only bike but don't knock it until you have tried it. It is not the only way but it is a way. Enjoy.