I am a big of the Joomla Project. I think Joomla has great potential. I tried to install the Joomla Ecommerce package from the VitueMart's website and had several problems from the start. One of the biggest problems was that I could not see the administrator menu bar in the joomla admin site after i the install.
If i was going to install this on my own site, I would love to test it out an report bugs. But since its for a customer, I don't want to upset them and I am going to use a more tried and tested shopping cart.