Since this doesn't seem to have been posted yet,
here's a link to the only review I've found so far for the new
DA 55-300mm.
They seem impressed, especially with the resolution and lack of distortion, and their grades for "subjective quality factor" are fairly impressive. Which is all reassuring to me, since my lens arrived yesterday, and I haven't had a chance to give it a decent test yet. From what I've seen so far it does seem better than the Tamron and Sigma 70-300mms I used previously. Having the lens start at 55mm is definitely useful, and personally I don't miss the "macro" ability of the other lenses.
Since selling my kit lens, all my glass has been "full-frame", so I was quite surprised by how small the 55-300mm is. This is a good thing and it doesn't seem to suffer vignetting. In terms of build quality, it seems similar to the 18-55mm kit lens, maybe slightly nicer. The focusing ring does feel very slightly rough or 'gritty' to turn, but no worse than the third-party lenses, and I much prefer the Pentax due to the ability to autofocus and then instantly go to manual without having to press any switches. Autofocus is definitely not fast, but that's inevitable with a body-driven lens of this spec, and I wouldn't personally benefit from SDM since I'm using a K100d. For those of you with SDM bodies it would have been nice to have the option, but then that would increase the price too.
So far it looks and feels well worth the money... now I can't wait to go out and use it
I will of course post samples once I have shots worth posting.