I am confused, however, about why 10.5 took so long to come. It seems to be an anemic upgrade overall. Perhaps iPhone and the big secret project took/are taking up a ton of resources...
Maybe because you're not looking at the REALLY cool stuff?
http://developer.apple.com/leopard/
Read the stuff in the Leopard Tech Series on the right. It's all the under the hood changes and changes for developers that have been taking a long time, and to be frank are what makes Leopard the most important release of OS X since 10.0