I've now had my 3DS for over a year (specifically since June 11, 2012) but before buying the system, I was a little concerned as to how it would hold up over the years. I say "years" because I spent because a system costing over $100, it damn well better last more than a year. The point is, my DS Lite officially died (sort of) when the plastic casing covering the right hinge finally broke off and could not take any more super glue, which is what my solution was the first two times that the hinge broke. I had other obvious concerns such as scratches and wear marks on the touch screen, dead pixels (although I never had the problem with my DS Lite, I do have 3-5 on my PSP) and long term battery life.
Next to the screen, and I guess the buttons, the hinge is the most important part of the construction for the 3DS. If the hinge is compromised, the top screen will wobble from the screen cable like an arm hanging from a tendon or a bit of nerve. Considering that I saw myself opening the system, playing for a bit, closing it, opening to play a little bit longer then closing it again for the night before putting it back on the charger, the hinge is a key element. Clearly what the system is designed to do. In reality, I probably open/close the thing close to 5-10 times any time I have it off of the charger. Those hinges are going are going to be seeing some serious action.
Presently, the hinges feel a little loose, almost as if I've been opening and closing the system close to every day. Which is what I've been doing. There is a little bit of a wobble, but that only happens if I consciously and gently shake the system back and forth while playing a game, which is something that I do not do. Most of the time I just have the screen open to the first "click" and not all the way back. I like a bit of an angle and having the screen all the way back makes it feel like I'm creating an obtuse angle. So yes, after a year, I have noticed that there has been some wear on the hinges, but not enough so that I am overly concerned that the hinges will break within the next year.
If the screen dies in any way, there's no point in having the system around. Unless you're the kind of person that has a use for parts, which some people do, just not me. I have noticed a little bit of wear on the bottom touch screen. Nothing out of the ordinary for a screen that regularly has a stylus scrying across it's surface nearly every day.
I should also mention that I do not have any scribble heavy games such as titles from the Wario Ware series. The World Ends With You has given the touch screen the most ware and even after 56 hours, the screen still looks pretty good. Theres still some give on the screen when using the stylus, which I will take as a good thing. As for dead pixels, I have not noticed any. Both screens work just as well as when I first bought the system and I haven't found that they get any smudgier than any other screen in our apartment.
In other news, I have not noticed any dead pixels on either screen.
This section will be entirely speculative. I have no data to back up anything I'm going to say here, but this is the Internet, so it's all okay. I haven't noticed any significant decrease in battery life. I know that "common knowledge" dictates that you shouldn't recharge a battery until it's either very low or dead because doing so will shorten the overall life of the battery. Everyone knows that right? Anyway, I will frequently play the 3DS until I get the red flashing YOUR BATTERY IS ABOUT TO DIE light and then I'll put the system back on the charger. That is what would happen in an ideal world. Most of the time I'll put the system back on the charger overnight after having only played for 30-60 minutes. Sure, there have been times where I thought the battery barely lasted an hour, even with the 3D slider either off or barely on.
With absolutely no data to back this up, I will say that I am happy with how the battery has been holding up.
After 461 days and 291.733 hours of use (combined total of game and application use), the 3DS has held up as well as I would have expected it to. The touch screen works fine without and dead pixels or dead areas. The hinges are a little loose, but that's to be expected after the aforementioned usage. I am happy.