I have had this camera for a few weeks after having used a pentax *ist DL and have been very impressed with it.
Build quality: The first thing I noticed was how solid it felt in my hands, given the price point of this camera I was quite amazed. To my mind it feels as good as the Nikon D80. The grip is comfortable and the buttons in sensible positions.
Key Specs: 1. With weather and dust seals the GX10 (and its brother the pentax K10D) is uniquely placed in the DSLR market to combat adverse weather conditions. Add to this the anti-dust system and you have a very effective system. Anyone with a DSLR who has suffered from particles on the sensor will tell you this is very very useful. I've taken thousands of images and not had to re-touch any due to particles on the sensor. It is slightly off-putting when you start the camera up and feel a bit of a shake though I quickly got used to this 2. Anti-Shake seems to work pretty well, certainly noticeable without it, although I don't know how this compares with other cameras systems. 3. 10MP Sensor, most people will not need bigger - I've printed off some A3 prints that I've been very happy with.
Handling: It feels great in the hand, very solidly built and has an array of buttons close to hand. Focus zones and metering zones can all be changed with external buttons. You do however have to go into the menu system to change the ISO, but you quickly get used to doing this. The white balance settings give you a preview of the impact different selections will have on the image, which is very useful, particularly when you deliberately choose an incorrect setting. I don't think the metering system works quite as well as my friends nikon, but on the whole was pretty impressive.
Image Quality: On the whole very impressive, although just like the Pentax, the jpegs do seem to be very slightly lacking some of the sharpness you would get from a canon or nikon. However, you really need to be looking at full size images to notice, and as most of the time you're not going for more than A4 it really doesn't matter. The RAW images are amazing, 22bit means lots of flexibility when you come to do some post processing.
On the whole, especially for the money, I could not believe how good the camera is. The biggest down side is the name on the front and lack of kit from Samsung, but there is such a huge array of past and present pentax stuff that you can use this should not be a problem. You are likely to get a few sniggers from the canon/nikon boys, but with an equally capable camera and lots of spare change in your pocket, you'll get the last laugh.