I am not a big fan of 3 column layouts, they tend to clutter up the page too much. In your case it may be the best to go with 3 but I would like to see it in a 2 column layout to compare. Overall nice content, I would just try and reorganize things a bit more logical. The banner ads on both sides of the page take away from the content in the middle. My 2 cents worth.
Install SEO pack for your cart to make it more SEO friendly where all the product URL will be included with keywords instead some weird numbers and syntax.
Wow, really let me jump right on that... As for the site related to this thread, its looks nice. Also not a big fan of 3 column layout, but a lot of major retailers use them. I do this that you have too many products listed in the middle column which is causing it to scroll to far down, most viewer wont go that far down the page.