I'm new here but I want to share something that made a big difference for me--you might want to experiment with the idea to see if it makes a difference for you too.
In my initial setup, I was using E-Junkies' default checkout buttons for credit cards, google checkout, and paypal. The first week my E-junkie cart was implemented, my sales were way off from my old cart (a different supplier). So I went back to my old setup and did an analysis of what the differences were.
At that point I made a few significant changes...
1. I added a line above the checkout form that was used on my old cart, it says: "Shopping cart contents (nothing is final until you submit your order, end of checkout)" The thinking here is that people might not realize that they are not committing to anything at this stage. On the default E-Junkie cart, I don't think that is clear.
2. I made it a bit more clear that you need to click the buttons at the bottom of the form check out. The old buttons were simply labeled with logos--that doesn't work for everyone. First I added the line that says "To Checkout: Please select the appropriate secure order form to the right" which is roughly what my old cart said.
3. And then I redesigned the buttons and made it very clear where each button takes you.
"Order by Credit Card Online"
"Order by PayPal Online"
"Order by Google Checkout"
Here is what it looks like today: http://www.ideabook.com/store.html
Yes, it sounds like fluff, but the effect was immediate and significant--sales were back up to speed. Though the E-Junkie cart has not increased my sales thus far, it is now in place and working and I can tweak it to try to improve results from here.
If you try it, I'd love to hear what effect it has...