I've used Virtuemart on a few sites, but no more. It would be good for small operations, like non-profits, however the PayPal payment module has a major error in that if a customer abandons the process after they visit paypal, the order processes as if they had paid. There is a patch written by an individual developer, but in my experience it only works in development. Once you think you are good, and try to go live, it fails.
The reason why Virtuemart is not appropriate for actual businesses, is that it requires the user to enter personal information before they can see the price with shipping and tax. This will lead to a high cart abandonment rate, because chances are the competition doesn't require this, and you will lose the order to them. Check the forums and the problem is often mentioned, except by the developers.