I've used advantage for almost 7 years. My vet advised advantage, he said that frontline while very effective, gets into the bloodstream to work. So if your dog has a reaction to it, it can't be washed off, that's why Tracy, your girl reaction lasted so long. I only put it on like every other month, and I haven't had a flea on my animals in that entire time.
Advantage is less effective towards ticks, but it just isn't a problem in my area. Also advantage can be washed off if there is a problem with it, b/c it stay in the the sebacious oil glands rather then getting into the bloodstream, with a degreasing cleanser, like Dawn dish soap if there is a problem, but will stay on with regular shampoos so you can still bathe.
But I think evey product has that oddball dog out there that shows a reaction to stuff from time to time!