I think the only "problem" (not much of a problem really) is explaining to flight attendants that I don't need any of the forms they are passing out to the passengers. Many don't appear to know what global entry is, then I point to the advertisement inside the airline's magazine or to save myself the time of explaining, I sometimes just say "I already have it taken care of".

Another time I got off a flight and was walking to the Global Entry kiosk, an airline employee was at the front of the entrance into the immigration hall stopping passengers to check their passports/status to see which line to direct the into, I proceeded to walk around her since she was blocking the way into the global entry lane, I was pointing at the global entry sign and she said "ah ok you have that global thingy".