OAuth Dance -- "client identifier invalid" with Salesforce.com

So over at CloudSpokes we use OAuth for everyone that logs into our Database.com (Salesforce) org. It's been working fine for over a year but the last couple of days the OAuth dance have been failing randomly (5% of the time?) for one our our rails apps with the following error:

client identifier invalid

What made it so strange was that it had been working for quite awhile without any code changes for thousands of logins per day. I Googled around for the answer (couldn't find much at all) and even posted to the Developerforce security board with no luck (or replies).

I raised the question to Eric Holmes, one of the other committers for the databasedotcom gem, and he had the bright idea to specify the actual pod in the host instead of the generic "login.salesforce.com". After I switched the host to our pod, "na7.salesforce.com", I stopped receiving the oauth errors. I thought I might blog about this in case some else runs across the same issue.