We check this website, now sitebuilder.com is up and dont blocked for our system and other users of the Internet.
So, answer to question: Is sitebuilder Down Right Now? - NO! sitebuilder is up!
If you have problem with access to site sitebuilder, and domain sitebuilder.com is not avalible.
Clear browser cache and/or try other web browser
(Chrome, Firefox or Safari).