Thanks for the DIY - I changed my plugs this weekend, and it would have taken a lot longer without this guide. It took me longer than I thought, but I divided the work into two mornings, and was careful enough to avoid breaking anything for once - some bits had already been broken (by BMW).
A couple things I learned along the way:
Step 3: The wiring harness literally pulls straight out towards the rad. There doesn't seem to be any release clips.
Step 7: You need to (carefully) lift the brackets on top of the coils all the way up to a full 90 degrees. As it goes from 75 to 90 degrees, it is unlocking the wiring harness. Likewise, when you put it back together, the bracket needs to close down to bring the plug all the way into the coil. For some of the coils, there is not a lot of room to remove the wiring - but it's easier if you lift the coil partially out first.
Step 11: After replacing 3 plugs, I started the car for a brief time to see if everything was alright so far - you could do this after each plug if you want to know if there are any problems - but I suspect you want to keep the engine as cold as possible - it might affect the torque values if you change the plugs in a hot engine? Anyway, I didn't want to re-assemble everything just to find out I did something wrong on the rear plug....
Now for the old plugs - 100K (km) or 62K miles...they look ok to me, maybe they could have gone all the way to 160K. The plug from cylinder #3 is a bit suspicious, maybe some expert here can say. Car runs fine after the change, maybe a subtle improvement. I'll need a little time to be sure.