That it was phrased as a percentage is a little tricky. Consider someone who makes $50k/year versus another guy making $500k/year. That's a hypothetical windfall of $5k and $50k, respectively. If both guys do the same amount of inflating in an absolute dollar sense, the max is that of the lower income guy. That means one guy inflates by 100% of his raise, but the other guy only inflates by 10% of his raise. Year after year, the lower earner's net savings rate has gone down considerably more than the high-earners.
Anyway, I went back and forth between the 0% and 1--2% answers, and settled on 0%. After thinking about it, in the past, I've received some substantial raises, but definitely haven't inflated my lifestyle proportionally. After after getting into the whole FIRE thing, I've been on a slow but steady march of lifestyle deflation. So my SWAG is that I've never inflated my lifestyle by a whole 1%, but have maybe done 0.5% on occasion. And my current goal is to stay much closer to 0% than 1%.
In the spirit of full disclosure. If I was already FI, I might answer differently. I can only speculate how my attitude will change once I reach that point. One outcome is that I make a habit of lifestyle deflation, and I continue to discover more ways to be happy(er) without spending any more money. I would call this the "pure MMM way", because I'm convinced MMM's income could go up 10% and he wouldn't inflate his lifestyle at all.
On the other hand, it would be easy to rationalize, "Well, I'm already FI, and have everything I need, so why not indulge my wants a bit?"