I thought one of the requirements for entering on visa exemption was to have 10,000 baht equivalent, but I saw on the Washington, D.C., embassy website that you need 20,000 baht. So is it 10,000 or 20,000? 

Also, do they check for proof of accommodation?

As far as I know it is 20.000 baht but I am not from the US and no, never been checked or had to prove acommodation.

The rules, I believe have, for a long time, been 20,000 baht per person (or 40,000 baht per family) if entering with a regular visa or visa exempt. There is a reduced requirement of 10,000 baht (20,000 per family) if entering on the 15-day visa-on-arrival.

4 hours ago, BritTim said:

The rules, I believe have, for a long time, been 20,000 baht per person (or 40,000 baht per family) if entering with a regular visa or visa exempt. There is a reduced requirement of 10,000 baht (20,000 per family) if entering on the 15-day visa-on-arrival.

I think it also allowed equivalent in any 'major' currency to be shown if asked, on arrival.

In practice it seems that only "doubtful looking" characters have to show proof. I wouldn't depend on it though.

2 hours ago, overherebc said:

I think it also allowed equivalent in any 'major' currency to be shown if asked, on arrival.

Correct

I used to carry Thb 20 k with me as at one point I was making multiple trips in. Never asked to demonstrate I had the funds on me. The rumour is that if you look a bit on the dubious side / shabbily dressed they may ask you to demonstrate the funds but I’ve got no evidence of that. 

With over 30 visa exempt entry’s I have never been asked to show how much I have on me or seen any other travellers . Of course that doesn’t mean you won’t get checked but if you are normally dressed etc your chances of being asked are low.