I have learned after having owned numerous BMW's and working a few shops, that our cars (BMW's that is, I don't know about the Z4 yet) are quite easy to work on. Everything is laid out logically and is well designed.
For instance on a mid to late 90's Pontiac Grand Am you have to remove a wishbone engine mount and partially support the engine in order to change the serpentine belt. That is poor design. If I remember correctly, flat rate quoted 3 hours to do that that belt change. You can change a belt on most BMW's in about 20 minutes - especially the modern ones.
Another example: Chevy Cavalier (I may be wrong on the model - its been a few years) windshield wiper motor. Its mounted under and inside the passenger side front fender. If it goes out (and it will eventually - its American) you have to remove the fender. That's insane.
I am not saying everything on our cars is easy, but overall they are quite easy to work on. I appreciate that. Its one of the many things that has kept me coming back to the model. I know no one cars, but I wanted to reminisce about the old times.