I love the RescueTime-Beeminder alliance - it's magic. I set RescueTime to send Alerts when I've worked 4, 5, 6, 7 and 8 hours of Very Productive Time - so when I get tired, I feel good about what I did!

Adding some sort of rewarding Badge or Alert popup/text/email would make Beeminder even more addictive than it currently is. Seeing the graphs is a carrot; losing money is a stick. More carrots is always nice!