About the warranty, yes replacing the wifi card will void it. Unless your are extremely crafty at peeling stickers, you will have to rip off or puncture the greenish metallic sticker on the bottom of the laptop in the center. see comments below for more info regarding this. Basically, just be on the lookout for any stickers if you have a non-lenovo warranty.
@maxharleman:
1. Some people have suggested turning off ipv6. I tried it before swapping to the AC card and it did seem to make the drops less frequent. I won't pretend to understand how that even makes sense, but it's a thing.
1b. Some people have also opened up their y2p to find that an antenna or two had been unplugged. Of course, even checking this will void your warranty and is really only a way to possibly save $50 on the AC card. I personally didn't have any unplugged wires, so I don't think it is the root of the problem anyways.
2. I've disabled most power management garbage and notice no difference in battery life.
3. Intel maybe, Lenovo doesn't seem to give a beep about it, even with this 100 page thread about a major flaw in their flagship ultrabook. not that I can blame them on the hardware/software end of it as that's entirely up to Intel, but I'm sure their lack of communication or help for customers won't be forgotten when we're all shopping for our next laptop when the time comes.
4. Yes, hardware malfunction is certainly covered under any warranty that starts with a "w" they might give you the run around as they will with any issue, but it is certainly covered, just as a fried CPU or broken fan is covered. Whether or not a return is covered at all, as opposed to a replacement, I wouldn't know unless I actually saw the warranty. I bought my y2p refurbished from a 3rd party seller so I doubt it is the same thing.
edit: I don't know if anyone has tried this yet, and I'm not really up to the task of swapping my card again to test it, but it might be worth trying out the drivers for the AC card on Intels website. The two cards are very similar and those drivers seem to be a bit further along. I don't know if they will even install, but if anyone is feeling adventurous, it might be a thing they can test out.