The latest growlnotify in homebrew (1.3) fails on OS X 10.6 (Snow Leopard), because it’s a Lion-only binary.

marca@SCML-MarcA:/usr/local$ growlnotify 
dyld: Symbol not found: _kSecRandomDefault
  Referenced from: /usr/local/bin/growlnotify
  Expected in: /System/Library/Frameworks/Security.framework/Versions/A/Security
 in /usr/local/bin/growlnotify
Trace/BPT trap

Here’s how to fix it (thanks to https://github.com/mxcl/homebrew/issues/8316):