Google Apps is having an issue now affecting some primary and reseller customer accounts. The Organizations and Users tab won't load; it says it can't display and gives error #1000. This prevents you from performing many functions; I was trying to get on to rename a user.
I reported the issue to Enterprise Support. They updated their status page, where they describe it as an issue with the Admin control panel / API.
They're working on it but currently there is no workaround. I'll update again as soon as I hear of a workaround or resolution.
Update midnight Eastern: Issue resolved!