You can use a 4/3rds lens on a micro 4/3rds body with an adapter. In fact you can use a whole bunch of other lenses however not all features are available.
Just got a new G10 the other day. It'll be Evan's camera and I'll keep the GH1. The game plan at air shows now is I'll shoot video with the GH1 and Evan will shoot stills with the G10. We just have to figure out what to do with lenses. We have the 14-42, the 14-140 and a 45-200. The 14-140 doesn't have enough reach for our stuff and I don't want to buy another 45-200 when the new 100-300 is coming out soon (hopefully)
I gotta say - the G10 is one sweet camera! Very light weight and packed with all the features we could possible need for an incredible price! We used it a bit yesterday and it's a great camera. It's neat to see the evolution of Panasonic cameras
Here's a little slideshow of shots from the new G10. The colors it gets are amazing! These shots are all RAW and unedited except for slight sharpening.
A lot of the shots were in manual focus in a fairly dark nursery which blurredthe shots a bit. Next time I'll use a tripod!
