I am on my second, the screen developed a crack within the first week, after i bought it in January, I was able to get it replaced, despite MS crappy policy, however since then, its been sweet, used all day every day, I work out every day too.
I only take it off when I am doing tricep push ups, simply because I fear it could crack the screen under that kind of pressure. (I have heard of peoples cracking...) But when i am using all other weights, cardio, etc, I dont worry about it.
I do not even bother with screen protector, I just use some standard clear tape, and it fits like a glove, if the tape gets scratched i simply replace it easy. I have tried several screen protectors, but they always start to peel. Total cost 0
Otherwise i never take it off except to wipe it, charge it, or shower. But screens in 100% condition, strap looks a little scuffed through wear but otherwise not bad at all.
I actually have more trouble with my phone than the band.