All my lenses just doubled in length ....

Image quality with a 2x digital mag or a crop of the image afterward yields the same result. I wish Sony would not upscale the digital mag image back to 16meg, but I understand their reason.

The main advantage, for me, is in framing. I use my C3 & Zeiss 24mm while traveling and have used 1.5X to 3x at times with good results. about the same as cropping afterward. But anything you do to the original information (image) degrades that information.

Canon A2E, Sony R1, Panny TZ5, Nikon D5000, & NEX C3/Zeiss 24mm E Lens