If you have a PowerShot G3... don't rush for the G5 like I did... re-think about it... :)
The CA is worse than on the G3, and there is much more noise (even at ISO50).
Also it is noticeably slower. But that's because of the larger filesizes (I shoot almost always in RAW).
If you have an older camera or no camera, go for a G5, if you have a G3, stick to it.
I made a good deal out of my old G3, and found a new G5 for less money than a new G3 ;)
So I switched :)
I also bought a Wide (~28mm) and Tele (~245mm) converter (each with it's own lens adapter, so I can switch them in a jiff).
Check out my latest submission for an example of a ~28m