K-7 vs. A200 - no surprise it's a major change, almost entirely for the good. Much of what I found important enough to buy the A200 in 2008 is still here: onboard image stabilization, dynamic-range boost, and the image qualities that only big sensors can deliver. Their sizes are nearly identical, which ironically is why I switched: Sony's A700 features were quite similar to the K-7 but it's too large for my comfort. Sony's recent trend has been small camera = limited features, so given that I'd need to re-learn a new Sony interface it might just as well be a Pentax interface. For the same size (and a price difference <$200, two years later) I have all the features I seek: durability (e.g. weather seals & long-life shutter), versatility (more exposure options, 1/8k second shutter speed) and features I didn't have before (mirror lockup, metering follows AF point). I also have live view and a movie mode; these two features DID NOT factor into my decision, Sony - sorry to break it to you. I've tried LV twice with mixed success, and haven't shot a movie yet in a month. Nice that they are there for my future learning, but not needed at present.
AF lenses - the DA 16-45 was a surprising choice on the surface, as it was replacing my Sigma 17-70. I really liked the range on the latter, but had always wanted an affordable 16mm lens, whether fixed or zoom. I had hoped to catch an A700/16105 kit but had no luck, and the camera was too big in any case - but now I was sacrificing a lot of reach for that 16mm spot. Since the samsung sensor is actually a tiny bit smaller than Sony's, the 16 v 17 is even less vital - but I liked the price and the features so there it is. And the results are amazing, as sharp as the 17-70 but with higher sensor resolution to make it work. Losing f/2.8-3.5 isn't a big deal, less important to me than losing 100g off the lens weight. If the K-7 weighs more, at least its lenses can make up for it. I've owned some impressively sharp lenses in my Sony time, most notably the Minoltas 35-105 Macro and 100-200 f/4.5; the DA 16-45 fits in the same class of glass to my mind. That might be the four extra megapixels talking - but in any case it's very very good, and holds up well on a 14M-pixel camera.
For telephoto, my DAL 55-300 arrives next week; it is highly regarded in reviews by both owners and websites. The DA would be better still, but a few less grams (and dollars) persuaded me to forget its lack of quick-shift focus and non-metal mount. It could be a short-term lens for me if Pentax announces a weather-sealed version of this lens, but the DA and DAL are optically identical and are both under 450g, quite light for such a range. It's similar to the Tamron 70-300 that I attached to the A200 and which has closer 'macro' ability. We'll chat later about how the two compare in use. I used the Sigma 55-200 for a month with the Pentax, which outperformed Sony's well-liked zoom of identical range (both good for sharpness, but the SAL55200 had far more pincushion distortions at the longer end).
With three lenses (16-45, a 50 prime and 55-300) I will have a very versatile kit (though no weather-sealed lenses) that should do me for a while!
MF lenses - for now I'm scrimping a bit on the 50mm prime, having picked up a bargain Rikenon-P f/2.0 lens at auction. I had a Pentax-A 50 for a bit, but a shrewd bargainer took it from me along with the 55-200. The Ricoh lens is a touch sharper in focus but has spikier bokeh, so the images as a whole were slightly better with the Pentax. I also have a Chinon 28mm and a Rikenon XR 135, both f/2.8 lenses that work very well (though it's hard to prove they are sharply focused on the default focus screen, the AF confirmation does give guidance). These lenses have served me well but are not auto-aperture, so M-mode only for these
Last but not least - well, maybe least - I have another Ricoh P lens, the Rikenon 28-100 f/4.0 Macro. It's a fun but heavy lens (605g), and it's lived a full life i.e. the front elements can shift a bit and fall out of focus. It's fun to play with but can be a little frustrating if you aim up or down. And like all of the MF lenses from long ago, flare is quite debilitating so I must carefully keep light from hitting the front glass. As long as that's done images are quite good.
That's it for now, thanks for listening!