I've gone back, sorted the comments by 'new', and upvoted everyone who commented they did the survey since I took it, and upvoted everyone who did it before me. This way I've upvoted everyone, and they got more karma. It took me three minutes. If you spend a substantial amount of spare time on Less Wrong, it might be worth it for others for you to do the same. The more people who do this, the more karma everyone gets. Also, it can act as an incentive for people to take the survey for karma even if they're late to the game.