It's clear that I've been doing this for a little while, now; the daily trials and tribulations of a commuting motorcyclists are starting to not faze me so much. Case in point: yesterday, on my ride home from work, a city bus decided to merge into my lane. I was in the far left (carpool) lane, and this big articulated bus started a merge without signalling as I was passing him. I'd been watching, I was ready, and I got on the horn, shifted to the far left edge of my lane, and got ready to avoid either by accelerating or, more likely, pulling just out of the lane into the breakdown lane. It turned out the driver just hadn't seen me; he looked when he heard the horn and aborted his merge until I was past.
The interesting thing, for me, was the fact that my heart rate didn't even pick up. The problem was solved in seconds, and the ride went on. This is a common problem we face, and though it can be highly dangerous, perception of the traffic around us and being ready to act at all times can pretty much deal with it.