If theymos receives a valid subpoena that can be enforced in the US, he will have to give up IP address information per the order. If you are being accused of "promoting bitcoin" in your country, theymos will almost certainly fight any subpoena he receives for your information, however he may or may not be successful. I also don't think a US court would enforce a subpoena if you were only "crime" was "promoting bitcoin"
Right. Though you shouldn't trust anyone with stuff like this; use Tor if you're concerned. In DTalk's case it's especially important, and simple proxies are likely insufficient, since HTTP/SOCKS5 proxies are unencrypted and a man-in-the-middle could apply eg. HTTPS stripping attacks.