Do you have any problem with discoloring/yellowing over time?
No, I haven't had any problems with discoloration at all but then again, I haven't really had it that long nor do I keep my phone in a jeans pocket or anything that could transfer color. The clear back isn't porous at all, so I I think maybe just cleaning it off with a little rubbing alcohol or windex occasionally would keep it looking nice.
The only issues I've had are with the front edges - they are slightly rough (for better grip, I guess) and it irritated the tops of my pinkies since I am a two-handed texter and anchor my phone with my pinkies on the front edges and after a couple of weeks straight using the same case, I noticed that my left pinky was pretty scraped up so that's why I switched back to my D-Tech cases with the smooth rubber bumper. My husband really likes his UAG cases (he texts with one hand so no anchors needed, lol) and has no complaints whatsoever.