Update: If you’re not a fan of having to remember to hold down the “6″ and “4″ keys each time you re-boot, there’s a fix courtesy of Netkas.org:
Edit this file:
/Library/Preferences/SystemConfiguration/com.apple.Boot.plist
Change this:
<key>Kernel Flags</key>
<string></string>
To this:
<key>Kernel Flags</key>
<string>arch=x86_64</string>
Boots into the 64-bit kernel like a charm every time on my MBP.
