CG, did you use Imaging-Resources side by side comparison feature to look at the pictures they take? That's usually a good barometer of which one is the better option as the proof is in the pudding. Right off the bat, I noticed the SD870 has a better macro. Looking at sample shots I also noticed that the SD870 had sharper, and bolder colors at 200 ASA. And while both invite a noticeable amount of noise to the party at 1600 ASA, the amount of detail lost to the FX500 is unacceptable. In low light, you'll with you hadn't bought the Panasonic.

I'd go with the SD870.