Shopping Cart and ECommerce Software
Solutions from PDG Software, Inc.^®

If you are using Authorize.Net ,you may be experiencing intermittent problems on your web site resulting in the message “AIM returned unexpected data.”
Due to formatting changes in the information that Authorize.Net is expecting to receive from your web store, you will need to enable a configuration variable in your PDG Commerce program to correct this [...]

Another interesting article from Practical eCommerce about increasing conversions and keeping customers on your site…
http://www.practicalecommerce.com/articles/1350-Conversion-15-Reasons-Why-Consumers-Will-Leave-Your-eCommerce-Site
Any other suggestions?