I believe it's a Delta-owned thing. It's basically a place to sit down and have [very] light snacks (bagels and cream cheese in the mornings, at least) and beverages. There's comfortable chairs and it's quieter than sitting in the terminal. I also believe that very soon they plan on having WIFI as well.

Even if it's owned by Delta, I don't think you have to fly that airline. My dad never does anymore. It is, however, a yearly fee. Only worth it if you fly quite often, which my dad does.

*edit*
OK, then, United I could have sworn it was Delta-related...