Have you tried doing a 'soft reset' of the TripIt app? I'm assuming the iPad can do this like the iPhone... You minimize everything, double click the round button on bottom, and across the bottom it shows all apps that are running in the background. Hold down on one, and they'll all start wiggling and have a - in the upper left. Press that - on TripIt (and others if you want), and the next time it opens, it will be somewhat refreshed.

I try to periodically do this and kill all open apps on my iPhone, and it seems to help the performance of everything.

Anyway, I just added a trip yesterday. When I first opened the TripIt app today, it wasn't showing. I went into another trip, then went back to the main screen, and then the new trip was showing.

I still print off copies of all airline, hotel, car rental, and other important items I'll need for a trip, and keep them in a pocket folder my backpack. But if I run into issues, usually the info from the TripIt app is enough.