Originally Posted by NeverSatisfied 
Well for one thing, once you set any amount of EV comp, that adjustment remains until you physically reset it- even if you shut the camera off in between. I found that out the hard way yesterday at the park on an overcast day. I had +2 EV set (just messing around the night before), failed to notice, then wondered why I had to use ISO 800 to get a proper exposure. Took a minute to figure out.
That would have given you a 4 stop over exposure (assuming ISO 200 as your base, 5 stops with ISO 100 as your base).
The thing that confuses me is how they say setting a POSITIVE number for EV comp actually results in UNDER-exposure, and vice versa. But then I've heard people on this forum say that with certain lenses they always dial in +.3 or +.7 EV comp due to a tendency of the camera to underexpose. Aren't these two ideas in conflict with each other? Or does Pentax just not know how to explain it?
That's not how it works. EV+ increases the exposure to allow more light. EV- lets less light in. When you are shooting snow, you dial in EV+ to brighten the snow to avoid the snow being gray. When shooting black, you dial in EV- to darken the item to avoid the black being gray.