In my opinion US immigration officials are usually quite polite when compered to some European immigartion officials. As a someone from East Europe, I can tell. Finnish Immigration Officers used to be worst. They humiliated me personally every time I entered (or exited) Finland until Estonia joined EU. Harsh questions like: "What did you do in Finland!?" (while leaving Finland) were norm. One of my friends was searched by Finnish customs and videotaped and then told that he can go - without any apology. Since Estonia joined EU 2004, they canŽnt legally ask those questions any more (freedom of travel within EU) - or treat their neighbours like trash - and actually Finnish immigration officials now just do not say anything at all or kind of are trying to be nice.
However, last month I went to Holland for 2 days and IO at Schiphol airport demanded to see how much money I have. I declined of course (freedom of travel within EU) and he said with much pleasure that he will refuse me entry then (I complained to his supervisor and he was of course overruled).
All in all - I have seen lot of disturbed individuals - who clearly want to humiliate passengers - working as a European boarder guards. So far I haveŽnt seen them on US ports of entry. US immigation officals may have questions, but IMHO they are polite or at least neutral.
Of course, I travel much more within EU than to/from US.