I just got my new US passport from Bangkok Embassy, and wonder if i can just go straight to the airport with the new & old passports and fly out, without visiting Immigration Office? My tourist visa has expired anyway, so there's nothing to transfer. I have heard conflicting reports - a couple of friends flew out without problems, but nobody knows for sure. Any 1st-hand reports or opinions please?

Cheers! Yuri.

You can leave and show both passports on departure from the country. No need to go to immigration.

Immigration offices don't transfer visas, even if they are still valid, they only transfer the permit to stay stamp, which in your case isn't necessary. When you leave the country the IO will transfer your current entry/permit to stay stamp to your new passport and then stamp you out of the country.