Just got around to trying out some experiments, and so far it seems to be pretty robust. In most of the things I've tried, it lit immediately and was consumed entirely, no need to re-light (except for the wet test, I'll mention below). I used a lighter, so I can't be certain other methods (flint, bow, etc.) will ignite it as well, but given how quickly it lit they might not be much different.
- Loose crumpled ball: Burns quickly, all gone in about 15 seconds.
- Folded into a tight square: Burns very slowly but steadily. Took (approximately) five minutes to burn out. This seemed pretty optimal for starting a fire.
- Folded into a tight square, soaked in water for a while: After squeezing out most of the moisture, it seemed somewhat dry so I tried to light it. It lit but wouldn't stay lit. I unfolded it and let it sit to dry for a couple minutes, then refolded it. After that, it lit and burned pretty much the same as the dry folded test.
- Crumpled in a ball for a while: Pretty much the same as the tight square, though it might've lasted slightly shorter and burned with a larger flame.
- Folded and kept on top of a warm oven for a while: Doesn't seem to have run or melted; it didn't stick to or run into the paper towel it was tucked inside. Discolored from the heat but lit and burned without any problem.
- Folded in my wallet: Going to just leave it in there for a while and see if it affects how it lights. By this point I'm assuming it won't have much of a problem, but I'll update this if it has any effect. EDIT: It's been a while, but as I recall, the paper that had been left in my wallet for a few weeks basically worked the same as fresh paper. Overall effects might vary based on brand and pocket temperature, but it seems a viable way of storing some emergency fire starter.
Other notes are that the tightness that it's folded affects how much ash is left behind; if it's folded lightly, it all but disappears, but the tightly folded square leaves a significant chunk of ash behind. I wasn't able to detect any chemical or plastic smells while it was burning, but that doesn't really guarantee for me that it's not making any toxic fumes so I figure it's safer to avoid inhaling around it while it's lighting. The brand itself may matter -- for all this I used Reynolds.