Have you tried center-spot AF?
Are you using a half-press and seeing if you've got focus confirmation before taking the picture?
Have you tried shooting without zooming, but just getting closer? (On my G9, my minimum focus distance gets larger the more I've zoomed). Alternatively, have you tried Macro mode? Your minimum focus distance at the Telephoto end of the lens (manual: p.95) is just shy of a yard (at the wide end of the range, it's 2cm).
Have you tried using a tripod and timer/remote to make sure it's not camera shake? (remember, the more you zoom, the faster your shutter speed has to be to avoid camera-shake blur). Alternatively, are you
holding your camera correctly? Are you getting the vibration warning (the little hand)
Have you tried backing off from the extreme edge of the zoom range? Zoom lenses are sometimes softer at the extreme ends of their ranges. With a superzoom like that, I'd doubt it's at its sharpest all the way out.
Have you tried stopping down? Lenses are rarely at their best wide open. If you're going to use the flash, anyway...