I was having a dig around looking for some space on the root file system using a rather great filesystem viewing tool called "Disk inventory X" and leaping out from the picture was a single 670MB file. This single file accounts for about 18% of the size of Leopard.
Tucked away in the Alex voice Speech library folder was the data definition for the new very smooth Alex voice. Do try it out using the System preferences -> Speech -> Alex just to hear how much an improvement the voice is over the previous very robotic attempts.
The techical details are ...
Macintosh: $ ls -l /System/Library/Speech/Voices/Alex.SpeechVoice/Contents/Resources/PCMWave
-rw-r--r-- 1 root wheel 701743856 24 Sep 02:06 /System/Library/Speech/Voices/Alex.SpeechVoice/Contents/Resources/PCMWave
The amusing bit is the file data type identifier at the start of the file which is
Macintosh:Resources $ od -c PCMWave | head
0000000 meow \0 001 \0 006 \0 \0 \0 0 002 303 Q 000
[Removing voice file instructions removed - May 2010]
This file was trimmed down for Snow Leopard which as a % of the size of HDs is not so bad.
PS I later found this Blog entry of Billyoregon who previously discovered this file using the same technique.