Update (3:30pm EST): It's alive (again)!
As we hang out on Twitter today, chatting about innumerable different things (prime example: trying to figure out what our accounts would be worth at auction), we're seeing quite a lot of reports from people of being unable to use their GrandCentral accounts. And given that our own repeat attempts to pay a visit to the service's main page (the GC blog, though slow to load, seems to be active), we can vouch for it's temporary "out-of-commission-ness."
For those unfamiliar with the service, GrandCentral is a service from Google that gives you a virtual phone number that allows you to direct it to automatically ring any phones (home, office, mobile) configured to the service when called at one primary central number.