Tyre pressures
#2
IMO, you shouldn't be messing with tire pressure for ordinary driving in order to adjust the ride comfort or handling. If you have 22" wheels and find the ride too stiff, that comes with the wheels/tires at no extra cost. Stick with what's listed on the tire pressure label that's pasted on the driver's side B-pillar -- it's a matter of safety.
#3
I run them soft though. On a 33x12.50r22 or 35x12.50r22 I typically run 28-30psi. That gives a great ride quality, but it will sacrifice some handling characteristics. On factory tires you might be able to get that low, but probably not quite that low without having strange tire wear or handling issues. You also run the risk of pinch flats the lower you go, but that's probably still plenty of pressure to prevent that in most cases.
As a side note, the factory recommended tire pressure takes a number of things into consideration. Tire wear, handling characteristics, optimal fuel mileage, load handling. If you aren't trying to optimize all of those things at the same time, then you can play with the tire pressure a bit without worrying about sacrificing too much in terms of any one variable.
However, if you want to think about it from a lawyer's angle, improperly maintained or equipped vehicles leave room for a challenge to liability. But, that is a whole other discussion...
#4
The treadwear argument is a valid one. Tires run at incorrect pressure develop telltale wear characteristics that are discernable to your tire dealer, and this could possibly void your tire warranty. And as tires wear in this manner, stresses transfer to your vehicle's suspension components. The legal issue is also legitimate. Almost every accident I read about involves some hapless driver who "lost control", and this is difficult to refute if your tires are in bad shape.