Apparently, whatever problems existed have been fixed for now. This is apparent not only because my own Vonage service is working again, but because new posts complaining of outages have effectively ceased on two of the best resources for tracking Vonage issues.
Those resources, as well as the specific threads that tracked the problem where the "Is Vonage down again? thread on the Vonage VoIP Forum and the Vonage having problems again thread VoIP section of Broadband Reports.com.
The next time your Vonage service coughs, I recommend that you visit and perhaps post your travails on one or both of these forums. Funny thing: as I have seen time and time again, these forums seem more on top of service issues than the Vonage site itself.