I don't know what happened today. Normally I love this app, but for whatever reason today, it became completely unusable. I have an iPhone4 running ios5. Today, the app repeatedly froze and crashed. And when it did finally run, it would not respond at all to taps on the screen. I was on a 400 mile trip, and this was frustrating to no end.

What causes this kind of behavior? It's been very hot out and the iPhone did feel a little warmer than usual, but other apps seemed to work fine. Please help.