This fix seems to work great for me, my MBP I7 now shows four cores in logic with activity spread across all 4. Haven't spent much time with it but yeah seems to be all good, I wish apple would update logic properly.
Yes, well I went to my regular store (Macs and other things Apple) in Oslo, armed with the benchmark test on an USB - stick. The friendly seller allowed me to do a quick test, and luckily they have Logic 9.1.2. installed on all Macs there. The i5 MBP 17 managed only 19 tracks, with the Activity Monitor showing all cores active..... Very depressing, I was hoping that my four year old MBP C2D (2 GB RAM) would have a LOT less "grunt" than a shiny new MBP 17.... The difference is WAY to small to defend the heavy investment. I´m really disappointed with this, but so glad I found out before I ordered the new MBP! But: if there´s anyone here who can convince me into buying the i7 MBP 17 please tell:)!!
I've had a different experience ... My i7 MBP under logic 9.1.1 ran 21-22 tracks in 32-bit mode. Then, I applied the terminal hack and got all 4 cores displayed in logic (still 9.1.1) and my performance jumped up to 28 tracks! Plus, I haven't restarted my machine in about a week! I'm a happy camper