Here's a few very well written articles explaining exposing to the right and way you'd want to do that.
I'm new to the Pentax Digital Line, but been started shooting Raw 10 years ago with Leaf and Phase One backs on my Sinar LF.
Underexposing in digital is bad ('mm kay) Blowing the highlights in all 3 channels is bad ('mm kay)
So you'd want an exposure that is just this side of not being entirely clipped. If you are shooting raw, and using Lightroom, or another ACR shell, then you can restore the highlight detail, even if you blow one or two of the highlight channels. Of course it's best to not clip any channel in your highlight, but it can be recovered if you have info left in one or two of them.
You don't want your histogram to be in the middle or to the left, when you adjust your exposure in post, you will be left with more noise, banding, and beginning to posterize, and you're ultimately left with an image that just doesn't have the tonal information to make a decent print.
Here's a short article on the "sunny 16 rule" and exposure in general
Understanding-Exposure
Here's a short article on Histograms
Understanding Histograms
Here's an article on the "exposing to the right" theory
Expose Right
Here's one on restoring clipped highlights using a saturation mask in photoshop
Restore Those Clipped Channels
In Lightroom, there's a slider to restore highlights (again works best if there's info in 1 or 2 channels)
I'm merely posting these links and opinions, in case any of you are interested in exploring this further (proper digital exposure), everyone has to figure out what works best with their style and workflow and gives them the best results. But most of the digital photography books that deal with RAW and Photoshop books that deal with RAW goes into this as well and some with more detail. When I started in digital, I shot fabrics and clothes, and had a very bad time with noise, banding, you name it. It never occurred to me to shoot like this (I was used to shooting transparencies) But then I read a book that suggested this and what I looked at on my computer looked awful, until I made my final adjustments, then I wound up with images that had a much richer, vibrant and much extended tonal range, and finally getting rid of my worst problems. Digital sensors are much much better today, but I think it is still good to at least know about this and have it available as a tool you can use if and when you need it. I know a lot of photographers who expose like this all the time for every image, and I try to do the same myself.
I admit that my underexposed images look real nice on my screen, but I still do a lot of catalog and print work, and the difference at that point is literally night and day (especially in CMYK 4-color process, Yuk). If I was shooting for the web on the other hand, I wouldn't bother with it at all.
happy reading!