Heh... I've noticed that too in my rental. It's really nimble, and at speed it gets a little squirrelly. Mainly because I'm accustomed to the Jeep, I think, which is pretty soft in steering. The Corolla takes just the slightest touch to switch lanes. Usually... it's because I meant to. I think it might also change lanes if you just think about it real loud. :-)
Mmm... nice responsive steering.