Did you succeed in installing LilyPond on Lion? How?
After downloading the (precompiled) LilyPond, I am getting:

In plain text:
LilyPond Error
An unexpected error has occurred during execution of the main script
ImportError: dlopen(/Applications/LilyPond.app/Contents/Resources/lib/python2.6/lib-dynload/objc/_objc.so, 2): Symbol not found: _objc_sync_notify
Referenced from: /Applications/LilyPond.app/Contents/Resources/lib/python2.6/lib-dynload/objc/_objc.so Expected in: /usr/lib/libobjc.A.dylib
And yet I duly have:
ls -l /usr/lib/libobjc*
-rwxr-xr-x 1 root wheel 1997152 21 Jul 01:27 /usr/lib/libobjc.A.dylib
lrwxr-xr-x 1 root wheel 15 21 Jul 01:28 /usr/lib/libobjc.dylib -> libobjc.A.dylib