Is there a Wordpress shopping cart that.....
 

Is there a Wordpress shopping cart that will allow the customer to buy blank products such as Mousepads, T-Shirt, etc... Then allow the customer to upload their artwork and/or text to be printed on the product?

I cant think of one off the top of my head but you might be able to grab something like

Market press http://premium.wpmudev.org/project/e-commerce/

And ask a PHP or WP person here to code that in or you might even put a request in with WP-MU and see if they have all ready done it.

WP custom cart?
Of course there is, several, but they don't work worth a shit.

Thought you were a big time marketer.
Guess not ...

Get that custom packaging made yet?
Wanna buy some?

a simple file upload via a product page would work

I could have sworn I saw a cart for WP that was built for people wanting to do T shirts and other screen printing.

I allowed uploading of art and would pass it along with the order after completion.

i would have to do some research on it.