Just installed my M-sport steering wheel last night, Getting the airbag to unclip was difficult. I got the first clip undone within about 5 minutes or so, so you'd figure the second one would go even faster, but it took about 15 mins.
I wanted to share a tip on getting the connectors on the back of the airbag to come loose. This was the second hardest part of the process for me until I figured out the trick on how to disconnect that plug. It is designed with a locking mechanism. If you look at post #2 on this thread, 3rd pic shows that connector which is green and black. If you lift up the black part (gently) with a small flat head screwdriver on both sides, the whole connecter will practically fall out of the socket on it own. I did not lift it off the main body of the connector completely, i only had to get it to slide about half way up, and it stays in place cuz of a groove and a couple of pins that keep it all together even when you loosen it up. Alternatively, there are a couple of grooves on the top of either side of the black piece that you can stick you fingernail under and lift it that way.
Total install time for me was about an hour,
2008 E90 328i - Sparkling Graphite/Terra/Dark Burl, 6MT, Sport, Premuim, Fold-down seats, iPod/USB(6FL). M-Sport Steering Wheel, ZHP M-Sport Shift knob, Euro fog lights. Euro Split Armrest