Another idea - I don't know how difficult this would be - would be to have some way for websites to give freebies to people who have tipped more than, say $5 in total to anyone that month. The website owners would get two benefits: people would be more likely to tip them, and they would get more traffic (because you would provide an 'if you liked this...' feature to sites who did that). This interacts well with the 'split $X at the end of the month' feature, because tippers would then round up in order to get the freebies.
