The ProLite Plus or a closed-cell foam pad would work much better for winter camping. The NeoAir only has an R-Value of 2.5 whereas the ProLite Plus is 3.8, an important factor when camping on cold ground or snow.

Chad, I believe it has an emergency blanket-type sheet inside which is supposed to reflect the heat of your body back on to you.

I have a similar Big Agnes insulated air core. I've slept on snow with it before, and it was pretty chilly. However, if you throw a closed cell foam mattress on top of it, or an insulated thermarest, you'll be extremely comfortable and warm. My winter pack always gets a little bigger/heavier because of this.

It all depends on your metabolism. If you're a warm sleeper, this could work as a winter pad, however, I would caution you against it. I personally have slept on a Prolite 3 in winter without issue, although I was a little chilly (acceptable to me due to the size and weight of the pad). The NeoAir will be similar. A better option would be a NeoAir and a Z-Lite in combination. Both would weigh less than a standard pad, and having two insulative barriers will increase the R-Value. As well, the Z-Lite can't puncture so even if the NeoAir does, you will still be left with some insulation. Having the two will give you about a 5 R-Value. This would work for me in most conditions.

This is a very individual question. I would recommend checking out some of the gear forums at Backpacking Light. There's a huge amount of chatter over this pad. The consensus seems to be coming down towards 3-season use, but what works for one may not for another; we're all snowflakes, etc. I will be buying a Neoair for myself, but it won't replace my Exped Downmat for winter trips.

Whenever I go camping in winter I take my prolite 4 sleeping pad, which has an r-value (insulating/warmth value) of 3.8 I believe. According to thermarest this pad has an r-value of 2.5, so just a little bit less, but amazing for having no internal insulation at all. I have used my pad on the snow itself, in temps down to 0, with no cold spots at all. I would guess this pad would work quite well in winter all well...