If you're going to be waiting around for more than an hour, I'd go for the day pass. The PIT club is still one of my favorites, as I'm in there at least once a week. The Club agents are awesome, and I love Joann, the 80+ year old bartender! They're starting to spruce up the club a lot - new blinds, and talk of new furniture and new carpeting. It was decently crowded last night, but you can still find a quiet corner to work or relax.

Being on United in F, you're not automatically granted club access. If you're flying int'l on UA, then I'm not 100% sure...they'd probably let you in.