As a Pentax user (35mm) it pains me to say this, but as far as I can tell Pentax simply aren't in the same league as the big boys in the DSLR stakes. I haven't used one enough to really compare (any DSLRs I use are borrowed rather than owned by me) so I'm relying on other people's tests, but most comparative reviews while not saying there's anything horribly wrong with the Pentax seem to suggest there's no particular reason to go for one unless you have a lot of Pentax lenses. Which, seeing as you'd never heard of them, I'm guessing you don't.
I have two complaints about Pentax DSLRs that to me seem so obvious I wouldn't even need to see one to know they would put me off buying one.
Firstly, none of them go below 200 ISO. Now if the various Pentax *Ists produce images at 200 ISO that are as good as the 100ISO or lower offered by Canon and Nikon then I withdraw my criticism, but I can't see that being the case.
Secondly, Pentax make a series of cameras - *ist D, *istDS, *istDL, *istDL2... that appear to be almost completely identical. Some have a bigger screen, some have minor improvements and changes, but nothing major. They've now released two new models, the K100D and K100D, which include a 'shake reduction system' but otherwise don't seem to offer much different from the *ists (anyway you can get shake reduction in the Konica-Minolta Dynax/Maxxum cameras, which are cheaper since the company's pulled out of the photo business and which won't be a dead system because it'll be supported by Sony when they take over where KM left off). In short, Canon and Nikon offer entry-level DSLRs, advanced amateur DSLRs, semi-pro DSLRs (I don't like made up words like Prosumer :mrgreen: ) and pro DSLRs. Pentax offer entry-level DSLRs. I personally wouldn't want to buy into that system with no possibility of upgrading to a better body.
I really hope I'm wrong on this, because I like Pentax and don't think we should all have to choose either Canon or Nikon. But I can't really see what a current Pentax DSLR would offer you over a similarly priced model from either of those companies.