I use those Admirals' Clubs regularly. They are OK. The food and drinks options are poor, but the showers are pretty nice. There are also some comfortable chairs which recline, which might be good for sleeping, although they can go quickly. The quiet rooms generally are quiet, but they don't contain the reclining chairs (from memory).
It costs $50 for a day pass, so you can decide if that's worth it to you.
Assuming you are in Terminal 3, it's also worth checking out the Virgin AmericanAmerica gates along concourse L, which have powerports, and the new Mexican place near Gate K8 or so (best food in the terminal).