I have stopped trying to get perfect scores on captchas. Instead, I've been testing to see how many errors I can get away with. This is a frivolous act of resistance, as the bots clearly don't need my help anymore.
It's purely anecdotical, but I'm convinced that Google CAPTCHA (which I don't see more often only because I rarely use Google Search) punishes me for being fast. I can half-ass it or do a perfect score, but if I'm done with it in less than 3 - 5 seconds, I'll only get another puzzle as a reward.