Whew, one helluva a mod you got there. Looks interesting enough, haven't gotten a chance to implement it but may sometime soon. Only thing I'd like to add is if your good enough with regular expressions you could use apache mod_rewrite and setup rules for easy urls, like:
www.example.com/xcart/customer/product/34
34 being the product ID. Which is good for search engines especially, that and it just looks nicer.
Anyhow, thanks for sharing the hard efforts!
