Though by the numbers it has a worse noise profile than the TZ5, the higher resolution helps produce a generally better looking image at all ISO sensitivities. You can see the detail quality drop off between ISO 200 and ISO 400 because of blur. The ZS3's photos still show Panasonic's characteristic blotchiness across the entire sensitivity range, but it's only really visible under limited conditions, like fine detail on a flat background under low light.
While I generally wouldn't recommend using over ISO 200 on the ZS3, depending upon image content, you can get away with photos up to ISO 1,600. Here, you can see the color noise and aggressive blurring, but the text is sharp and the photo could be used at small sizes.
Overall, the ZS3 produces even, accurate exposures. It does have a tendency to clip highlights in higher-contrast light, however, and lens flare can produce the effect of a haze over photos shot in bright light.