Okay - these should be working perfectly again.
We had a honeypot set up to stop spammers from bombarding the site with deluges of spam comments we have to sift through and delete. Because traffic is being filtered through a cloud proxy now, everyone's IP addresses were showing up the same for the honeypot module, and it thought that everyone submitting a comment or contact form query was submitting from the same IP address, one generating mostly spam comments, and just started blocking everybody.
So, we shut off the honeypot module, and commenting and contact forms are working again (albeit now we need to also delete 100s of spam comments per hour from the approval queue, while sifting through these carefully and making sure not to delete real people comments - we're working on changing some server settings so we can use the honeypot again, once IP addresses are being displayed as their appropriate addresses again and not as our proxy's IP).
Chase