None that we're aware of, and our Sysadmins get an instant alert on their cellphones whenever one of our servers goes down or stops responding. We've also got a fully-redundant architecture now, so a problem with one server or other piece of equipment cannot take the whole system down, although things may slow down slightly as other servers take up the load. Maybe there was a transient network routing issue between your ISP and our datacenter at that moment?
If the stall only happened when you entered a zipcode in the cart, and you're using a USPS rate-lookup shipping calculation method, then there may have been an temporary issue with USPS.com or their rate-lookup API, or a bad/typo'd zipcode can stall the lookup for a while until USPS responds that no such zipcode exists.
