Thanks for taking the time to write up this tutorial. I did just realize (and it's a shame) that the only place where we discuss editing invoices is the developer's guide... probably the last place the regular user would look.

I'm curious if you'd mind updating this to include a link to the docs:

http://www.ubercart.org/docs/developer/246/invoice_system

And posting it as a tutorial in the following section of the user's guide so it doesn't get lost in the forums. Just click the "Add child page" link and you can stick it in!

http://www.ubercart.org/docs/user/561/tutorials

btw, that's a sharp looking site! Do you have any estimate on the # of products in the catalog? It seems quite extensive.