It's good to read about things like this (not the evacuation or bomb, but the experience of going through it). I know there's a lot of scenarios that are talked about and discussed, and they're really good mental excercises for us armchair quarterbacks (or cubicle commandos, in my case), but listening to first hand experience from someone that's actually gone through it is much more useful.

Also, giving out too much information over a PA system might not be the best idea. Most of the ones I've heard sound like the speakers at a drive through window. I'd be lucky to hear maybe 50% of the words, and my desk is directly under a speaker. It's probably better to give simple one or two word announcements than detailed explanations that could be misunderstood. If I heard anything that sounded like "bomb" or "explosion", I'm sure those are the only words people will hear, and might cause a major panic.