Planet13 - 5:33 pm on Aug 12, 2011 (gmt 0)
I would definitely set up a funnel in google analytics to see where most of the sales are being lost in the checkout process (if the checkout process is more than one page length).
I really recommend a blog called getelastic.com since they feature all sorts of usability studies for improving conversions.
Also, is your traffic coming from the right countries? I get a lot of traffic from countries that we don't ship to and the visitors from those countries do seem to add things to their cart only to abandon them.
I hope this helps.