I have the Panasonic P46G15 installed for one week now and I'm very happy with this device. I bought a Panasonic Blu-Ray BD60 at the same time and both are very well integrated. The integration is also quite good with my Yamaha YSP 3000 sound projector (HDMI connection). Even my old Panasonic VCR can be operated smoothly through the main remote, thanks to the old Q-Link protocol (ancestor of the Viera Link).
Needless to say that the image quality with a Blu Ray disc is absolutely gorgeous. DVD's upscaled on the BD player are very good as well. But the best surprise is the quality of the regular TV picture. We are watching mostly Swiss TV channels and it is sometimes difficult to see any difference between the standard definition channels (TSR, SF. TSI) and HD Suisse, the high definition channel, which is accessible thanks to the integrated HD Sat receiver.
So far, the TV is not connected to the Internet or to my PC (actually, an aluminium iMac). So, I have not tested the Viera Cast or BD Live or iMac connection to show pictures or play music on the TV. No need for the moment, I'm very happy with the tV even without all these functions.