Would've posted it last night, but it was late and i was tired...
Disclaimer: I am not responsible if you brick your phone, as with all leaked/official but not your carrier OS versions, continue at your own risk
Note: This will only work for Intel Mac's...oh and no support for Snow Leopard I think, you're welcome to try it though I guess.
Note: I updated to the most recent BB Desktop Manager as well as updated the to the most recent Wine via the internal "Check for Updates" option.
Step 1: Download the OS build
Step 2: Make sure you have X11 installed. If not, insert your Mac OS install disc and well...Install it! To find out I just went to Spotlight and typed "X11".
Step 3: Download "WineBottler"
Here. The download includes two programs "Wine", which will let you run windows programs on the Mac; and "WineBottler" which will supposedly repackage an .exe into a .dmg (haven't tried that)
Install into your Applications folder, they provide a shortcut in the download so all you have to do is drag and drop. Very easy...
Open "Wine", nothing will actually open but you should notice a little wine glass up by your clock/wifi/bluetooth indicators.
Step 4: Right click on the OS .exe file, select "Open With", then select "Wine". A window will pop up giving you two choices. Either to run in a particular location, or create a .dmg. Select the first option and note the location as this is where you'll go to find the files. Then click "Go".
It will run thru some things and then the Install program will come up as if you double clicked the .exe on a windows computer.
Step 5: Run thru the Installshield Wizard. I did not run the AppLoader but I'm sure it would work just the same. I left the box unchecked and clicked "Finish".
If you are installing an unbranded version then skip to Step 9
Step 6: Now remember where you installed this to? If not thats ok, just go to Spotlight and search "drive_c".
Step 7: Go to drive_c, Program Files, Common Files, Research In Motion, AppLoader...Delete the vendor.xml file
Step 8: Not sure if it was necessary but since I have Tmobile, I also deleted VCastMusic.alx, VodofoneMusic.alx, VZNavigator.alx from: drive_c, Program Files, Common Files, Research In Motion, Shared, Loader Files, 9700AllLang_v6.0.0.461_P6.6.0.137
Step 9: Plug in your phone and return to the Apploader folder, run loader.exe.
I didn't time it but it took a few minutes...Once the phone was up and running it offered to play a video introducing the new 6.0 and offered to run through the setup wizard. I exited both and all my apps, accounts, etc were loaded already from the sync it does before updating. The only thing you should note is that if you have contacts saved on your sim card, just go to the Contacts app and it will ask if you want them imported to your contacts list.
It's going to take me a little time to get used to 6 vs 5, but I like it...Gives me the feeling of a new phone, enough to hold me over until TMO gets some of these new BBs this year.
If I get bored, maybe I'll make a guide with screenshots...but really it was easy enough...I mean I figured it out on my own, so surely you can.