I might as well answer as well:
1) I tried using a screen protector, but really, it diminished the quality of the lower screen for me. So, while I do have a little bit of wear on my bottom screen due to those DANG FRISBEE COMPETITIONS from Nintendogs, it's not noticable while playing a game. That's generally the thing too - it will accumulate a little wear. But it's not bothersome nor that noticable when playing the game. Sure, when it's powered off you can notice it, but why the heck is your DS not powered on then to begin with?!
2) Just like what Starshifter said. There's a little storage slot on the back of the DS. When your stylus is in there (and it does have a little like, "lock" to it when you slide it in, so it doesn't just fall right out), you can't tell it's in there. It's that unnoticable.
3) It's pretty durable. Yes, I would agree that the join areas are probably the most susceptible to damage, but I've dropped my DS several times with no damage there. Though, on the lid that covers the bottom screen when closed (which I love - when I had my PSP I hated how the screen was so "out there" if it wasn't in use. Plus I don't need a carrying case and I'm not constantly wiping my screen either, so another plus for the DS), I have a nice little cut/gash there. I call it my Nintendo DS's battle wound. It adds character
Hope that helps.