no link handy, but a similar thing was tried with email before. You had to offer points for someone to read your mail, and readers would natutally read the highest-paying emails first. The results sounded cool, similar to what you were predicting-- everyone got more conservative with others' email-redaing time. With the email version, you "traded points" by reading (or replying? I forget) your mail.

I'd love to try your calendar version!