We are currently designing the shopping system for a client and for that I research the cart process. I see numbers of 5-6% conversion (is that 94-95% cart abandonment...?) for big ecommerce websites.
I think conversion & shopping cart abandonment are different. Correct me if I'm wrong, but I think conversion is the percentage of people who buy when they visit the site (i.e. 1% conversion is 1 person buying from 100 people who actually visit the site).
People who put things in the cart and then decide not to buy do not get counted in the conversion rate.