http://uxmovement.com/buttons/why-ok-buttons-in-dialog-boxes-work-best-on-the-right/

Takeaway: place buttons at the bottom of the dialog right-aligned, with the primary action farthest to the right. Don't left-align secondary actions, it makes it harder for the user to compare them with the primary action.

Update: Interestingly, this site demonstrated success with left-aligned buttons for forms.

http://www.lukew.com/resources/articles/PSactions.asp

Maybe it matters what the content above the buttons is and how users scan through it? The visual path tends to be top to bottom on the left with forms, but left to right zigzagging with text.