Are US dollars accepted in Thailand? For anything?

Generally no. The baht is the currency of choice.

They are accepted for exchange to Thai baht.

For spending money, if not using credit cards, the Baht is used. We did find, however, that our guides and drivers were more than willing to accept USD when we ran short of Baht and there was no ATM available. But the local currency is what you should be using and available at ATMs that are found most everywhere.

I have seen it occasionally in places where the purchase is large (e.g. in the hundreds of dollars) and the clientiele almost exclusively western.

For day to day use however, never.

Shade

Thai Baht. If someone takes USD they would not give a good exchange ( unless it's a very large purchase and you clearly have nothing but USD ) as they have to go and change it at a bank or exchange place anyway, so all round better just to change to Baht.