enigma1 - 10:33 am on Jun 14, 2010 (gmt 0)
As ken_b put it the more steps you have for the checkout the higher the number of abandoned carts. I don't want to go around to different domains and pages to complete a purchase.
Also knowing features of payment gateways, there are many which handle the verification reliably without the need of an extra Vbv step. Certain processors in their cpanel/details indicate if the order can be processed safely by checking the shipping address with the one entered for an order.
The simpler the checkout the less mistakes customers will make and therefore more sales for merchants.