For interest’s sake, here’s my graph of Mac OS X build numbers v release date for Tiger and Leopard. This assumes a Leopard release date of 15th October.
I guess things to note are that the gradients of the graphs seem roughly the same, so the rate of development seems unchanged (no dramatic improvements in software development methodology or tools in the 2 years (I guess that includes XCode 3 :)).
Also, it seems that Leopard will have had about an extra 150 builds by the time it’s released compared to the Tiger release build. At the time Apple announced the delay of Leopard due to the iPhone (2007-04-12) it was 186 days before October 15th. At the time of that announcement the Leopard build number was about the same as at which Apple shipped Tiger.