The Sony is actually a CMOS sensor, not CCD's. I have heard that both their own strenghth and weaknesses but have not had enough experience with a CMOS camera to make a qualified judgement yet. There is a good article on the operation and differences for each sensor type
HERE that helped me.
The GS500 is a true 3ccd camera. You can read the Cnet review and get user reviews
HERE.
The HDC signifies High Definition Camcorder, it has the ability to record in 1080i. Be careful here though, I purchased a 3ccd camera in March, and while shopping I was looking at high def cameras but was scared away from them after seeing many complaints from high def camera owners about the lack of editing software that supports high def footage. The impression that I got was that decent high def editing software will not be available until late April into May at the earliest and will then be ridiculously expensive.
I found this out by reading up about AVCHD M2TS files which is the high def format Sony records into. Most programs convert this back to Mpeg2 which defeats the purpose of having a high def camera.
Hope this helps, good luck!!!