I've known a number of truck drivers and I've seen even more than that. Generally speaking, as a group, they are better drivers and more aware of the road than the average driver on the road. Not all of them are, and some of them do make stupid mistakes or drive dangerously. Sadly, from what I've seen, even the safest ones get flipped off and honked at just because the car driving too closely behind them apparently thinks the truck should be driving faster.
The financial information is pretty spot-on. Some truck drivers are making $40K (or even more than that!). The shabbiness of this depends on where they're based, of course, but it can be pretty comfortable. Some drivers make significantly less than $40K. It's a function of mileage and experience, for the most part. I'd say $500/wk is probably lower than average, but it's certainly not unheard of. Especially right now (I hate the phrase "in the current economic climate", but it's kind of relevant right now) loads are getting harder and harder to come by and the further ones tend to be the first that go. The miles just aren't there and this can kill the driver's family's finances.
Really, when it comes down to it, if a driver runs you off the road, call the number on the back of the truck (please, have a passenger do it if there's one in the car). But if a truck is just slowing you down a little bit, I know you in particular may know that there's no cause to flip anyone off, but this knowledge seems to be lacking in some people on the road.