Someone gave us an almost empty canister - it had about 10 toonies in it (yes, I'm canadian - toonies are two dollar coins in case people aren't familiar). With it, came an article. It's at FI's place (our place as of this weekend!), so I can't copy out the whole article, but the jist of it is:
every time you make love, put a loonie ($1) in the canister. when you have too much, put it in an account and keep adding until you can go on an all-paid for vacation with your spouse.
I thought it was kind of cute. The gift giver said that they use toonies to make it grow faster:P