I am flying United today out of McCarran and just found there's a new lounge in the D Gates!  So excited!  I have a Priority Pass membership, so I have free access to select lounges, and this is one of them.  I chatted with the staff... they've been open since June, and there's one in the new terminal as well.  It's a small lounge, but they have a decent beer selection (Asahi!) and some unique snacks (pita chips & hummus).  Friendly staff, free wifi, and a FANTASTIC view overlooking the concourse where people arrive from the shuttle.  This may be my favorite airport lounge yet.