Currently http://google.com/purchases is redirecting to https://xlocal.google.com/files/access_denied.html. Hmmmmm... what do you think that means??

and in case you can't access https://xlocal.google.com/files/access_denied.html this is what it says...

Access Denied

Only Google employees and other authorized parties can access xlocal.google.com. If you believe you should have access, please click here for tips or contact xlocal-supportgoogle.com.

And https://xlocal.google.com/ redirects to:

https://www.google.com/accounts/ServiceLogin?service=sierra&continue=https%3A%2F%2Fxlocal.google.com%2F%3Fupgrade%3Dtrue

i.e. the "continue" URL is https://xlocal.google.com/?upgrade=true

My guess is that the https://xlocal.google.com/ address is being used for internally testing the soon-to-be-released GBuy / Google Checkout / Purchases upgrade...

BTW, this URL is also being discussed here:
http://googlesystem.blogspot.com/2006/06/google-purchases-almost-ready.html