Actually, the ZS5 and ZS7 both came out in June 2010. The ZS7 is way more expensive, comes with a bigger screen, and GPS.
There is also an SZ7, which came out Jan 2012. Caused me some confusion.
Here's a great site I've found and used to compare just about any camera you can buy. Used it to compare the cameras for the above info:
DPReview.com side-by-side