While there are still some issues, the low ISO sensitivity noise on the GX1's JPEGs is visibly better than the rest of the G series, though the in-camera processing could still be a bit better (see subsequent slides). In good light, you can shoot JPEGs up to about ISO 400 without serious detail degradation, although even at ISO 200 you can see some softness.
Noise, low ISO sensitivities
Even at ISO 160 (the GX1's lowest), shadow areas still display the blue-channel artifacts that tend to plague Panasonic's JPEGs, appearing as yellow blotches--look at the text on the left side. (It's a lot easier to see the problem if your monitor is calibrated to Adobe RGB rather than sRGB.) Processing raw files makes a big differences in clarity even at this low a sensitivity.
Processing, ISO 1600
You can see how soft the GX1's high-ISO-sensitivity JPEGs get. Processing them as raw looks grainier, but I prefer it to the mushiness of the JPEGs, and they look pretty good for this class of camera.