I'm usually pretty good at getting ready for games but I haven't had the time to prepare for tonight's Pathfinder game. I'm usually quite casual about game prep, but then the games I usually run aren't as involved as Pathfinder - I'm used to running simple systems for larger groups, such as Star Wars D6 or Dragon Warriors and a much more complicated system requires a bit more attention.
The saving grace for me is the fact that my gaming buddy Jason helps with the general in-game rules but, as he's one of the players, I need to keep 90% of the details away from him. And I'm still getting used to CR ratings.
Usually, I only need about an hour to prepare an evening's gaming (I put all my hours of work into the pre-campaign prep) as I like to make sure I'm up to speed with where the players have been, what they're doing, and what comes next. I'm a sandbox game GM so I like to design situations and not stories so that takes a bit of pressure off, and I enjoy winging games anyway so that I can adapt to player choices, problems and moods.
Still - this is Pathfinder, so I hope that a lack of preparation doesn't ruin the evening's gaming.