The same "red shirt" protesters who forced a state of emergency in Pattaya (now lifted) by their invasion of the ASEAN+6 conference site have now gone after the Interior Ministry building in the capital, while the Prime Minister was in the building. He got out, and as a first order of business ordered a State of Emergency for Bangkok and the surrounding area.
That seems necessary, as the protesters have now massed at the Police HQ and at Government House. What comes next could get pretty rough if someone doesn't back down.
Until this comes to some resolution, best not to be going into harm's way. Consider this a Travel Warning and avoid unnecessary travel to or through Thailand for now.