Standard installation with sample data cant add to cart from "featured products" sidebar.
Not sure if its a feature or bug.
I Downloaded:
http://dev.virtuemart.net/attachments/download/983/VirtueMart3.0.12_Joomla_2.5.29-Stable-Full_Package_with_security_patch.zip
VirtueMart 3.0.12
Joomla 2.5.29