Hi - I'm assuming you're talking about the new range of Olympus micro-4/3 cameras as you can't mount any Contax/Yashica lenses on the original PEN. You can only add manual lenses which diminishes the options for the Contax N-series to 0. No adapter exists.
I have used both standard C/Y mount and G-series mount lenses on my E-PL1 and E-P2 bodies via various adapters. The Kipon for the G mount is particularly pleasing to use as it disposes of the fiddly knurled focusing wheel on earlier/cheaper adapters. The only issue is the same as for the larger 4/3 DSLRs - the 2x crop factor. It's great for long lens, portait or macro work but you have to buy the Zeiss 15mm to get a 30mm wide-angle perspective. And for the G 28mm f2.8, a lovely sharp lens ideal for the micro-4/3, you have to saw off the rear baffle which takes a bit of courage. But the results are worth it.
My best performers on the M4/3 are the 55 1.2 Planar (for portraits) but you have to use a tripod, the 50 1.4 Planar, 28 f2, 35 1.4 (portraits again) and any of the lenses above 100mm. I also get a lot of mileage out of the Yashica 55 f2.8 macro and the Contax Auto-Bellows with the 100mm f4.
There are also superb non-Zeiss/Yashica C/Y lenses from Tamron (SP range preferably), Tokina AT-X, Vivitar Series 1, etc There's almost no limit. Focusing is a breeze and the camera is always using the lens' sweet spot so super wide-angles are OK as edge definition is irrelevant.
