if you intend to run fenders, you'll probably want to convert. it'll make tire/tube changes, and gear changes if you run 2 in back, a lot easier. now, i'm absolutely certain that some FGF genius will point out that changing a tube on a track-ended frame with fenders is not only possible, but also will only take a few extra seconds of fiddling, etc. we all know that. but, it will be easier on semi-horizontal drops. plus, a converted frame'll more likely have bosses for fenders, which is helpful.

-rob