The very first live store based on Kartris is now online at http://www.thetozo.com/. This is running the v1.0013b build and the PayPal IPN payment gateway. We're continuing working on minor improvements and there will no doubt be some minor bug fixes in our present informal weekly release schedule. But the site is running stable 'in the wild' and we're happy with the performance of it on what is a fairly typical shared hosting package.
If you are interested in using Kartris for a site, the present code is certainly ready. Any bug fixes should be relatively simple; in most cases it will just require uploading the newest kartris.DLL. Any minor database tweaks required can be achieved with an SQL script we produce to cover any changes.
The upcoming holidays should be a perfect chance to spend a bit of time looking over Kartris without the pressure of customer calls and incoming emails.