The PAD protesters have surrounded the airport, delaying flights and causing headaches for tourists; but more importantly they are pressuring the government because the cabinet is now meeting in offices at the airport, because crowds have been surrounding the Parliament and government offices making it impossible to use those.
The situation is very tricky. The military coup worked only temporarily in 2006 for the Bangkok elites, they lost again to Thaksin's allies in 2007. That is the whole problem of this "revolution", Thaksin was ousted in a coup in 2006, but then his allies won in 2007, so the government's supporters (rightfully) believe they have a very strong claim to power. If the PAD manages to bring down government, there will be a lot of anger that could lead to civil unrest. There is an interesting article at the BBC on the class and regional struggle that are behind the political divisions (which I mentioned yesterday).
The army appears to be siding with the PAD, but what will they do if the government asks it to clear the protesters? They will probably refuse but what if there is internal dissension over this, with some officer attempting to rise in power by siding with the elected government, who agrees to do it. Could we see a breakdown of Thailand and a descent into some sort of civil war if the rest of the army side with PAD?
I doubt it. If things get too bad, the King can intervene and he has enough moral authority to stop serious troubles (I think). But things are looking bad for Thailand. Either the Bangkok elites accept the democratically elected government or they manage to take power and use the army to suppress dissidents. Let's hope they go for the former.