Did the quick turnaround (EWR-POS-IAH-EWR) this past weekend and wrote down "Transit" as the purpose of travel on my customs/immigration form. The immigration officer asked me to show her my POS-IAH boarding pass and stamped my passport with no issues. She asked me how much I paid for the ticket and said she hopes she can "do it someday."
That's funny - people like us everywhere!