After trying just about every trick in the book on my first mylar removal attempt (Fire!), I needed to find something...better for the left behind adhesive. I searched in the usual places, and came across "the flour trick". I see that it hasn't been mentioned on Pinside yet.
I scored a really nice Rocky and Bullwinkle last night. It had a full playfield mylar, and it was starting lift over a couple of the inserts. Anyways, pulled the mylar in the standard freeze spray method. Easy so far!
I lightly dusted the sticky left over adhesive with baking flour, then layed down a spray of Goo Gone Spray gel. I let it sit for 3 mins or so, then I placed a small pile of flour at the edge of the adhesive. It rolled up on itself, and I was done in about 20 mins.
This guy shows the premise in his youtube video:
My method of flour dusting, goo gone gel, and pushing a dry pile of flour into the start of the adhesive worked quite a bit better than his results, but his video gives the general idea.