For what it's worth, I just got a chance to try out my spare and jack. Last week I discovered a good sized screw in my tire, and that the tire was flat when I came back to the car after a work function at 10:30 PM.
I jacked the car up, slapped on the spare, and was on my way in literally 5 minutes. Without the spare and the jack, I was looking at either a) flatbedding the car to the BMW dealer and hoofing it home, in the rain, at midnight, or b) using the tire slime and ruining the tire and the TPMS sensor--figure a $400 bill, minimum.
As far as I am concerned, the $250 spare just paid for itself a couple of times over.
The E46 jack that I carry worked fine on the flat and level concrete in the parking garage. I'd hate to try and use it on a hill, though.
Attached is a crappy camera phone pic (and please ignore the bumper scrapes).
The car actually drove reasonably well on the spare. You could feel it pulling a bit, and I was extra delicate with the throttle and stayed close to the 50 mph limit, but all in all there was little drama.
EDIT: Since I took the pics upthread of the spare in the trunk, I bought the BMW branded Tire Tote. This is a good addition to the setup, since it keeps the wheel from getting scratched but more importantly gives you something to put your dirty road wheel in after you change the tire.