I had an otterbox for my storm. I never could get used to it. I don't have a job where my phone if on my belt(i don't think a storm with a otterbox would even fit in my pocket) would bump into much. Plus I don't make it a habit of dropping my phone lol.
Its a great product for those in need, but other than that, i found it pretty bulky. Plus the plastic cover that went over the screen for the storm wasn't attached at the sides, so that takes away a bit of the waterproof aspect. I would guess it had something to do with the click screen though, so might not be an issue here.
I can't imagine it on an evo. My buddy at work just got an evo and its a monster compared to my incredible. I like the screen size for viewing but really it just felt too damn big. Made my like my phone even more. I can't imagine an otterbox on it..might as well strap a netbook to your belt and go, lol.