Should build for 64 bit when running on 10.5 (10.6?) or later.
Spy driver should be 64-bit on 10.6. The 64-bit slice should link against CoreMIDI.framework, not CoreMIDIServer.framework. Also note the need to import CoreMIDI/MIDIDriver.h not CoreMIDIServer/MIDIDriver.h when building against the 10.6 SDK.
Fix other 64-bit unclean issues.
Started on this in branch '64bit'.
Finally fixed in 1.3. Master is now 64-bit and works with Xcode 4.