On the Surat Thani immigration website they have a rogue's gallery -- pictures of happy IOs and the people they've arrested (faces covered). Many are for overstay. Google Translate helped me to find out that there are people overstaying by years and years.
No, the US Embassy didn't know about that. I didn't actually get the Non-O until five months later, as I had some travel planned out of the country, and decided to wait until I returned from that.
Seriously? The US Embassy told me to do this and gave me a letter for immigration, so I went to Samui and they transferred it and charged me 500 baht! Grr.