When talking superzooms these days, I'd say the 18-250 is "da bomb"! I have the Tamron (got it the week it came out for a trip) and it's the same as the Pentax (confirmed by Pentax collector Jim King on DPReview, and by my Tamron rep). The Pentax is a little cheaper, and the Tamron has a much longer warranty (at least in the US).
I love mine and sold my kit lenses because of it. It's also my travel lens when I'm not traveling for photography. It was the only lens I took on my trip to Peru with my wife (a "once in a lifetime" trip), and I never felt like I missed a shot because of it. Indeed, I feel like I actually got
more shots because I didn't have to switch to the correct lens.
About the only area this lens falls down is in low-light action shots, which are a specialty area in my book anyway. I took numerous low light shots with this lens inside dark cathedrals and the shake reduction really helps with the extra stops, so you're getting an equivalent of ~f/2.8 if you're shooting wide (maybe ~f/4.0 at the tele end).
Are there compromises? Of course, but unless you're printing posters or doing extreme crops, you really won't notice them. PF is very well controlled. There's vignetting at the wide end. However, both of these are easily correctable in post processing.
Here are some examples taken with the K100D and Tamron 18-250.
You can see the full sized shots in my Flickr stream under the set marked "Tamron" and "Peru".