SCC covered their dog box conversion on a turbo'd Impreza 2.5RS about three years ago. This is what I [think] I remember in general..

Basically, they are ultra-strong geaboxes that use straight cut gears and often have no syncromeshes on the lower (if not all) gears. Designed to hold immense power, they necessitate a firm hand and relatively precise rev-matching or double clutching.