When performing checkstimation in Trello, you’re less likely to split the card into manageable list items and spend time estimating when you know you’ve got to then add them all up by hand. One solution is to drag this to your bookmark bar, and give it a click once your lists are split and estimated:
You can see a more readable version of the code on this gist
2014-01-21 Link and Gist updated to reflect recent Trello changes