I just got started with them a few months ago.
I kept having problems with my Gold Wing. (I've never had all that great of success with Honda bikes. They have caused me more problems and expense than any other bike that I've ever owned. So much for legendary Honda reliability! My old BSA gave me less problems than the other 4 Honda's that I've owned! The only good one that I ever had was a '72 Trail 70 that my grandparents bought when I was 12, and I ended up giving it to my nephew when I was in my 30's. As far as I know, it's still running.)
Even when it was running, it was so big that it was a hassle taking on little trips to the store, etc. So I wanted to find a little Enduro or some little cheap street bike for running around with. Unfortunately, I think everyone in this area got new crack pipes this year, and were pricing their motorcycles at 3 or 4 times what they're worth.
So, when I was helping my son look for a bicycle, I came across an ad on CL for a bicycle engine kit. (I didn't know there was a kit.) He wanted $250 for his CG kit, so I looked on ebay and found one for $129 and bought it.
The rest is history... (or lunacy!)