I've had this happen before, but never quite so severely. So I thought I'd post a warning.
As most folks know, the iPod is smart enough that if you unplug the headphones, it pauses any music that you were playing.
But if you're in the car and using a powered FM transmitter (such as those by Griffin), they don't plug into the headphone jack, they using the docking/syncing port instead. And you know what? If you're playing music that way, and you unplug it, it doesn't stop playing. This can be incredibly annoying, because unless you actually notice the little triangle in the upper right corner of the screen, there's no way you could ever know.
Unless you're like me, who has a smart playlist of "New Podcasts" tuned to erase things after they have been played once.
I woke up this morning to find my iPod almost completely out of battery, and every single one of my podcasts played (and, hence, gone). For the curious it looks like I get about 10 hours of MP3-playing battery life :).
That's annoying. Worse, iTunes has that self-managing "keep only unplayed podcasts" feature as well, so the act of plugging the device back in (to power it up!) also triggered a sweep of the files themselves, so they're gone from my laptop as well. If I want to get them back now I have to selectively go through my podcasts, remember which ones had unplayed episodes, go back to iTunes Store, and re-get the ones I missed.