Spontaneous Eraser Tool

Something that I've noticed over the past few years, first just in Flash, but lately I'm seeing it in Illustrator a lot too, is when you've been using it for a while and whatever tool you're using converts into being the eraser tool.  Sometimes you can select something else and go back to what you actually wanted, but sometimes you can't.  Sometimes I've had to quit out of the application entirely to get the proper tools working again, and if you wind up erasing something without realizing it, it can be problematic.  Most of the time this isn't too big of a deal, just annoying.  But I'm wondering how commonly this happens to others, and if there's a setting somewhere that I could change to stop encountering it.

Thanks,
~Sara