I have a G1 and GF1, I got a cheap 4/3 Nikon adaptor and it works well with these bodies – I already had a bunch of Nikon prime lenses 20,28,50,55macro, 180, and some zooms as well.
You have to tell the camera to operate with no lens , you can use the digital zoom for critical focus – left button , then center.
If you are looking for a prime and a bit longer , factor in the 2x
and you have a a lot of choice.
You do have to choose a mount to buy , any of the big names and the prime lenses are sought after , so maybe try Pentax, as there are a lot of compatibles , Ricoh for example , or perhaps choose M42 for the ultimate choice in cheap lenses.
Results wise – it works , it is a bit of fun and makes you more involved in what you are doing .
I refuse to pay the silly price for the pana 20mm1.7 it is not even stabilised , though it is very compact and would be great on my GF1.
Maybe ask around people you know to see if anybody has an old 35mm SLR going free and go for whatever mount that is?