Hi Stone,
I did wander what that plastic thing was for. I found it in the case. I knew it was for the strap but didn't know why (didn't read the manual again, did I?)
And no: I don't even know what L series glass is.....
Since I only used Nikon, I never bothered to find out what the Canon universes are like.
I know this camera uses FD lenses, though ;-)