Are faculty hiring committees overly polite on "denial" answers I applied to several tenure track positions this season. For some of them, I received an e-mail letting me know that I was no longer considered. That's cool and expected, since most of them were in US/Canada and I don't have any official experience working in neither...

My real question is: In some of those, they said that there were impressed by my resume/background/publications or something similar, always followed by a ", but". Are they being polite saying that? How much should I trust this kind of information?

(I could really use this kind of feedback to direct my search. It is not trivial to not over/underestimate yourself...)
This sounds like a standard US rejection - they may be sending this exact same text to all other candidates that were rejected. I do not believe you can learn anything from it and it does not reflect on you specifically in any way.

You can, however, try to get feedback, but it can be quite difficult - you must realize that the chances of getting good sincere feedback are not high. It is probably best to try getting this from someone with whom you felt there was a good connection or that this person was relatively open. Probably this person would prefer to do this over phone rather than by mail. You may also want to look at this question.