Their quality is actually really shoddy as well, and the free cards all say "print at VistaPrint" on the back of them. Not to mention the fact that they go to all lengths with retention emails after you place a single order (without having the option to opt-out) to keep people ordering more. They also charge a ton of hidden fees.
In short: If you want your business card to be a serious reflection of your business, DON'T use VistaPrint.