A real quick test with my Jupiter-8 50mm that I just got in the mail a couple hours ago. I was pretty excited to use the lens, and this is the fist thing I shot after I popped it on.
Overall I am very pleased with the Jupiter-8. If you can put up with how awkward it looks on the Gh2 (bit of an eye sore), you'll be pretty glad you did. I think I might end up liking it more than any of my current lenses and the fact that it only cost $40 on eBay is just ridiculous. It shows some real character that seems to be lacking in overly sharp modern lenses, and it gives off a really nice aesthetic.
The focus ring seems to be made by God himself, as it feels like it's gliding across a sheet of butter... It is really REALLY smooth and an absolute joy to use. I'm using a Fotodiox L39-M4/3 adapter which is working perfectly thus far.
I have yet to go outside and test this lens thoroughly, or do any sort of comparison, but hopefully I'll be doing that soon. This is my first vintage lens, and will certainly not be my last!