PayPal has posted notice of a major disruption to their service currently making checkouts unavailable for PayPal Website Payments Standard and Pro:
Notification: Major impact to APIs and www.paypal.com - Feb 18
Posted by PayPal_Updates on Feb 18, 2011 12:32:48 AM
NOTIFICATION: Payments via API and www.paypal.com are unavailable for most customers.
Sent Feb 18, 12:29 AM PST by VB
Start time: Feb 18, 12:11 AM PST (Feb 18, 8:11 AM GMT)
Estimated time for resolution: TBD
At this time, there is no alternative work-around.