I also can not get OS X to recognize my PowerShot A620 in Image Capture or iPhoto (version 2!). Then again, it's not a supported camera according to the list of compatible camera here on Apple's site. I blame Canon, mostly, for not making drivers of some sort with the Image Capture SDK. Honestly, I just don't want all this extra software on my computer just to download photos when I SHOULD just be able to do it in iPhoto.
EDIT: After installing the Canon software, the camera is still not recognized in CameraWindow, Image Capture, or iPhoto. Yay! Money well spent...
Is it an issue of USB 2.0 vs USB 1.1?