Jon Schick's reviews
7 out of 10 points and recommendedWeather resistant, very compact and reasonable performer for the pricePerformance a bit variable depending upon focal length and aperture
As with the 18-55WR, it's nicely put-together and feels a step up from many other kit lenses (including the older Pentax 50-200). Nice metal mount, and a thoughtfuilly-designed lens hood that allows the use of polarising filters. It's biggest selling point is its weather resistance (for which it has no competition at this price point), coupled with being truly pocketable. It's not much bigger than the 18-55.reviewed December 4th, 2009 (purchased for $170)
As for image quality, the review of the previous version of the lens on this site probably pretty much says it all. My copy of the 50-200WR is a bit disappointing when used wide open at 50mm (more so around the borders but you'd probably expect that), but is more than acceptable by the time you stop it down to F8. It performs very nicely in the middle of its range, and is still acceptable at 200mm - especially if you stop it down a little. At 200mm, mine comfortably outperforms the Tamron/Pentax18-250 superzoom, but is in turn comfortably beaten by the Pentax 55-300 - but then the latter is (a) much bigger, (b) not WR and (c) more expensive.
However, if you can find the 50-200WR at a good price, it's a compelling compact rainy day addition if you already have a weather resistant Pentax body. If you don't stress it to its limits, it can produce some great shots, and it'll allow you to use the camera on occasions when you would otherwise simply have had to give up.