Yep, it's available in K-mount, but without HSM. Think we have a couple of Pentaxians here with this lens, I've been considering getting it as well. B&H lists the same price for all mounts, so looks like you can't get it cheaper even without the HSM.
I had this previously. It gives a nice bokeh and images posseses very nice warm colours although occasionally there is a light pink tint. Its plus point is its more usable focal length vs the longer 50mm but be prepared for the weight as the lens is big and heavy (by pentax limited lens standard!)
Yes, airconvent had if previously, and I have it now. Sigma lenses seem to have a warmer colour rendition in general, not just this one. And what people say about this lens having wonderful centre sharpness and poor edge sharpness is true (though I think the real problem is that is has a very high field curvature). Not a problem at all if you're shooting with background bokeh in mind, but have to really stop down for landscapes. The size and weight doesn't bug me too much.
Some will rather get the FA31mm limited, but that requires a lot more budget. If got money I may upgrade to the FA31mm one day, or the rumoured DA*20mm... ;p
Yes, HSM works on those Pentax models that woefulwabbit has stated. But note that the K-mount version of the Sigma 30mm f1.4 is non-HSM. Unless they have made new batches adding in the HSM motor (I don't think so).