It usually gets mentioned on Lime Green Musings - here
. There's a thread in the Completely Off Topic section called "CBB down". You have to register for LGM membership, but the members are pretty much all CBB members too
There's also a CBB Facebook group, here
. I know not everyone's on Facebook, and that some people prefer to keep their CBB identities and real life identities separate, but it's an option.
Failing that, sites like www.downforeveryoneorjustme.com
will tell you if the site's down. Not foolproof, but usually quite reliable.