I've done this twice. Crashed for about 3 hours at the FRA RCC about 2 years back and slept for 5 hours at the DL SkyClub in HNL last month when on a layover going from NRT-HNL-ORD. I didn't have any problems with this and both times I simply grabbed a chair in the corner and slept.

HNL is just horrible for a long layover with no reasonable priced distant hotels in the nearby area, so after making the trek to Waikiki once before this time I just said screw it and stayed at the airport.

What I find disturbing is all the people that just sleep on benches around the airport. Sleeping in the lounge proves one has enough money to afford a hotel, but they're frugal and prefer to save it. Sleeping on a bench around the airport however is what vagrants do.