I am Yahoo! Addict, and Hybrid Theme Lover
Yes, I love Yahoo! its elegance display, and I love Hybrid Theme by Justin Tadlock for its simple, comprehensive, and more importantly expandable rock solid WordPress.com theme called "the hybrid theme", or it is named as "WordPress.com Theme Framework" by Mr. Tadlock himself.
The Hybrid Core Framework is easy to extend to whatever I want. For example, I can add more menus and contents wherever I can, as well as create custom posts and do other things just by adding theme support "add_theme_support();" As I repeatedly say in this blog, the Hybrid Theme Framework is also structured in a way that elementary theme developer will understand what these framework is doing for the theme.
I have added more things, pages, functions, widgets and menus, but I can still allowed to do so.
I do not want to bee too defensive to these framework, but I must acknowledge Hybrid WordPress Theme is the last one I have tried. For a few years I have been working with other theme framework, even I started with the "revolutionary work" on theme framework called "sandbox" at PlainTxt Blog, created by Scott Allan Wallick.
I did spend sometime to learn how Sandbox WordpPress Theme