I just came across this old thread, and read through it. I'm of the camp that I don't care how you say it....just convey the fact that you appreciate what ever you were given, or service etc. I was surprised by how many seemed upset by the no problem phrase. That phrase is used all the time by my two adult sons. Whenever they do something for us, and we say thanks, or express appreciation, their immediate reply is "No problem!" They've often told us how thankful they are for everything we've done for them over the years, and they mean that anything we need help with is no problem for them to do. It's become endearing to us to hear them say it.