I recently took my cross town fully rigid commuter / xc mountain bike and made it a dedicated single speed and it is the best decsion since i sold my half assed free ride bike for a full on DH rig. I rode XC a long time ago and it lost its luster after a while something was missing so I gravitated into down hill and love it. As a trainning tool my SS was born and I love it on the trail. It is a magical ride I recomend it to everyone, all the technology is gone no gears to think about no peaking a climb and thinking i could have done that better in another gear. No bonking and feeling disapointed cuz i made a bad gear decsion at the bottom and...... just coasting who would have known what i was missing insesantly spinning my cranks. Now when i am on XC trails it is me and the ground all guts no gears when I make a climb or tech section I didn't make last time I earned it and I know it.