I was just at the bookstore tonight, and the latest issue of Shutterbug has a long article specifically on using old/classic film lenses on today's digital cameras. They had a paragraph on Pentax lenses, and it sounded like they had good things to say about Pentax's old lenses on current Pentax cameras.
They did caution, however, about the A-mount, setting apertures manually, and focusing the lens manually.
If you get a chance, check out the article in the magazine. I'll bet it's also online, too.