Once I got to talking to my seatmate about travel and he mentioned he was going to the Presidents Club when we got to Houston. I managed to ask enough of a leading question (something like "is it nice?") so he asked me. Beyond that I'm a bit too shy about asking people on their way in to guest me. I don't think it's bad form though. I often guest people in to lounges if I get the chance so they don't have to feel shy like I do about asking