I can understand driving behind a truck to combat lead-foot, and to avoid arousing the ire of other drivers, but to be safe you'd have to be pretty far back. If you're far enough back that the truck itself is not a danger to you, other drivers might start getting irritated with your speed because they can't necessarily pass you and the truck at once. Best to hang back far enough that they can pass you one at a time if you're going to try this tactic on a two lane highway or other situation where passing is difficult, but then they've got to make two maneuvers, so I'm not sure you've gained anything with regard to not pissing people off.

In the photo on this post, the perspective of the camera shows that the following vehicle is too close. If you can't see the truck's mirrors, the truck driver almost certainly can't see you--and from that close, you can't see much of anything ahead of the truck. Likewise, driving beside a truck puts you right in the driver's blind spot and blocks your own vision of the other side of the truck.

As a motorcyclist, I do everything I can to keep as much distance as possible between myself and large vehicles, and there's no way in hell I'd let one block my vision like that. Riding near a truck makes it hard to see and hard to be seen. Add in the dangers of the truck itself, like tire blow outs or insecure loads, and they've got red flags all over them. I even avoid passing them without at least one lane between me and the truck if I can avoid it, and always pass as quickly as possible so as not to be stuck next to it.