I've added oil twice in 11,500 miles, not including the oil change a few thousand miles ago.
I haven't heard of any oil issues with the 640i.
Some 650i vehicles seem to have legit issues with oil consumption, but I think it's pretty normal for those of us doing it every 4k to 5k miles.
I get crappy mpg with my pure city driving - typically 11.5 mpg. I could get better if I changed the way I drive, but I have no desire to do that. As an interesting aside, I recently had a 528i (2.0 L, 4-cyl. turbo) for a loaner and got 15.8 mpg city on my usual route. Long live the V8!
