PayPal has posted notice (actually, several notices) of ongoing maintenance today:
http://www.paypaldeveloper.com/pdn/blog?blog.id=mtsupdates
These would not appear to affect any services relevant to our cart checkouts, but there's always a possibility of unintended consequences when they're doing things to their service. We'd rather mention something possibly irrelevant than fail to mention something that becomes unexpectedly relevant. :^) If you see anything weird happening with PayPal checkout today that seems to clear itself up later, this may be the reason.
