Jeff,
A few points as a follow up on your post.
To some extent, the filter/lens adapters defeat the purpose of the P&S, making it bigger and heavier. Because of the combination of the wide angle, and the lens extension in tele, the LensMate adapter for the G10, when used for filters, extends pretty far out and requires a 72 mm filter to avoid vignetting at 28 mm - so the camera suddenly gets a lot bigger and heavier. For use with tele extenders, however, only a 58 mm tube is needed as the camera is not then used in WA.
For the G7 and G9, the LensMate is smaller and uses a 58 mm filter, which keeps the size pretty reasonable.
Use of the Canon or LensMate adapters with just a clear filter (multicoated, and of high quality, of course) provides good protection against dust, mist or spray entering the camera through the lens. As the lens extends and retracts on zooming and at start up and shut down, it acts like a bellows and alternatly sucks in and blows out air from inside the body, bringing dust and moisture with it. However, if a LensMate (or Canon equivalent) is fitted with a filter on it, the lens is in a closed chamber, and the air from inside the LensMate is exchanged within the body and vice versa as the lens extends and retracts - no outside air is introduced under this condition, and so no dust is sucked in.
The LensMate on my G7 is also nice for a place to grip to help balance a large shoe mounted flash.
Several non-Canon tele extender lenses work very well on the G series cameras. Among these are the Olympus TCON 17 (1.7x, 55 mm threads), the Sony DH1758 (1.7x, 58 mm threads and requires a 58 to 58 mm spacer), and the Raynox 1540 Pro (1.54x, 52 mm threads). When an adapter ring for thread sizes is used, the thickness of the ring is critical to the sharpness of the lens/camera combination. For example, the 58 to 58 mm spacer, needed to prevent the lens from hitting the rear of the Sony DH1758 lens, needs to be quite thin to avoid soft corners in the image. A change of 1.5 mm (0.059") made a noticeable difference in sharpness on my G7.
--
Jerry