I've been intrigued by single speeding/fixed gear riding and bikes lately and am pretty keen on building my own fixie from an old-school roadie. Apart from the training benefits that can be achieved from fixed gear riding (strength, peddling technique, leg speed etc.) fixies are just cool. There's a pretty sweet website called My Fixed Gear where people upload images of their bikes - it has some nice creations. I also found this awesome clip on YouTube that really shows what's capable on a fixie! check it!