We have owned a GX1 for about a year and a few months and I have been meaning to write a review for ages!
Usually I use a Nikon D300 Body Only or a Nikon COOLPIX P310 Compact Digital Camera - Black (16.1MP, 4.2x Optical Zoom) 3 inch LCD but my mother bought this as a step up from her point and shoot and so I ended up borrowing it a fair amount. The beautiful thing about this device is how it slides right in the middle of a DSLR and a compact. It is small enough to fit in a large coat pocket but large enough to hold properly and to take proper photos with. The quality of the images is extremely good although the reason why it only gets 4 stars is that I do find the images get quite noisy very quickly so this is not great in low light. In fact I would go so far as to say that I'd rather have the P310 at night.
However the flexibility of being able to put different lenses on this camera makes it all the more wonderful to use. Using the 'stock' 14mm zoom lens you can get a lot done but I love the Panasonic Lumix G 20mm/F1.7 Pancake Lens which makes the camera tiny but still lets you take great images. It reminds me a little of a Leica M series camera when it has that on.
As I eluded the image quality is very good as long as you are not shooting at high ISO and it is super simple to use. It also has very little lag from pressing the shutter to taking an image which is a real boon.
The build quality is immense. My mum has dropped this a couple of times and although it is dented and the battery door is a little stiff, it still works perfectly. I am not sure my Nikon could survive the same punishment. I would say though, that if you are serious about taking some great images you should invest in the Panasonic DMW-LVF1E External Live Viewfinder for Lumix GF2, GF1 and LX5 It makes a huge difference to the shooting experience! Also you will probably want extra batteries if you want to use the brilliant video mode as it can get a little power hungry!
Everything about this camera is well thought out. The build quality is great, the buttons are where you'd want them to be and the menus are clear! Recommend