Hey! You should know that Panasonic has released a newer version of this product: the Panasonic HC-W580 .
The Panasonic W570 uses a secondary camera to capture simultaneous picture-in-picture footage without any editing. While the extra camera is certainly the headlining feature, the W570 also includes a few other perks, like a 50x optical zoom.
The W570 updates the W550. The features dictating video quality remain the same, while the secondary camera seems to be the biggest change. The W570 uses a 1/5.8" sensor, which seems a bit on the small side for the $500 price tag. That sensor will capture 1080 HD video at 50 fps and a 28 Mbps bit rate. The 50x optical zoom is an excellent feature, however.
The secondary camera allows for picture-in-picture recording, though the same effect can be achieved with a smartphone camera as well, opening up a few more possibilities for shots that a camera attached to the primary camera can't achieve. It's a new feature from Panasonic this year, and an interesting one at that.
With all the features though, the price on the W570 seems a little high. The Sony CX440 has the same size sensor and a better bit rate for under $300, though doesn't have the secondary camera or as large of an optical zoom. If the picture-in-picture function suits your shooting style, it's a good option, just be aware of the other affordable HD video cameras first.