I’d at it’s more like the gal I dated who had put 70k miles on her 4Runner, but didn’t know how to put it 4WD when we got caught in a blizzard. Most folks can find the shutter button. 
Also, as someone who worked in a color dark room making enlargements from both negatives and transparency, I DO consider shooting in RAW format to be pixie dust. It is amazing relative to film of yesteryear.
I have a full frame camera (5D Mk II) – anyone know how well this will perform with a extension tube like the Canon EF 12 II Extension Tube so that I can use an EF-S lens?
While it will work,you’ll get vignetting because it’s producing an image for a smaller sensor, and, according to comment #5 here, you’ll have trouble focusing at a distance.
This lens shouldn’t be used with a full frame sensor, unfortunately. Extension tube will cause vignetting as mentioned above.
This is a great lens for the money. As others have said, pics will lose some sharpness at full zoom and/or wide open. But it is very light and small compared to other Canon telephoto zoom lenses. I have the IS II version of this lens and I’ve found its sweet spot to be at f/8 for sharpness.
Here are a couple of moon pics I’ve taken with mine.
And a praying mantis 
Warranty: 1 Year Canon
Actually, you can register it with Canon (whatever country it’s marketed for) and they will handle it. The downside only being that there will be nowhere local in the US to service it under canon warranty, so it will involve lots of shipping to other countries for a few bucks saved. If you don’t care about warranty, and your local camera shop does your servicing, then there’s nothing wrong with grey market. You simply pay whatever rate the camera shop charges.
My entire body and kit lens was grey market, but it turns out it was made for the US market anyway, and is registered with Canon USA successfully. (I guess I got lucky?)