I'm seeing many comments stating that i7 users must use "cpus=1 busratio=20" for installation and boot up of OSX. Then, people are getting reboot issues when they remove these boot options even after patching DSDT (which isn't necessary if you're on Voodoo 9.7). Well, if your getting reboot issues after an install and you have removed all your boot options, then busratio is mandatory for you to specify.
Remember the i7 has no front side bus, so how can we calculate the bus ratio? We don't, we just use the clock multiplier That is probably why OSX is forcing us to provide it.
Thanks to wikipedia, we have these values in a nice table. Just look at the MULT column for your i7 type (may need to scroll up) List of i7 Multipliers
So, for example, to boot an i7-720QM with all 8 cores active under Voodoo 9.7 (if you're running into reboot issues) your boot options would be "busratio=12". You may optionally specify "cpus=8" in addition to busratio.
To make this permanent, you have to edit a string file in com.apple.Boot.plist . To edit open up a terminal and type:
sudo pico /Library/Preferences/SystemConfiguration/com.apple.Boot.plist
and find the following string:
<key>Kernel Flags</key> <string></string>
Change to (change busratio value to match your i7 version):
<key>Kernel Flags</key> <string>busratio=12</string>
Your i7 rig should boot without reboot issues and all 8 cores active (yay!). Some people purposely set the busratio higher, although I'm not sure it would provide any performance gains at the OS level.