I use the DOF preview button all the time... after a while, you begin to get an innate sense of what it's supposed to show, and you skip the step... it's more of a "reminder" that I'm at the F-stop I think I'm at, without taking my eye away from the viewfinder to double check the aperture...
Don't you see the aperture in the viewfinder?
I tried the Pv a couple of times yesterday but the main difference I noticed was it getting darker. It's of less use when shooting the wide I guess.