Google Apps seems like quite a bargain. Use your own domain name, and get ten free (and excellent) email accounts, plus google docs, calendar, and sites.
You can even use your free google site for ecommerce by adding the google store gadget.
But the limitations involved make it wonder if it's worth the trouble.
First, getting setup so that end user can get to your store by entering the "naked domain" can be quite a challenge. And keeping that domain from changing to a cheesy-looking "sites.googles.com/a/mydomain.com" can be even more challenging.
Then, as I understand it, the gadget will not allow buyers to make their purchases until the buyers sign up for a google account. And using paypal (a google competitor) is out of the question. To me, that just seems unprofessional. I would expect better from a real ecommerce site.
Please let me know if I'm wrong about any of that.