We’re wrapping up the first version of Twenty Eleven, and have one blocker: the header image is big. It’s HUGE, even. We love it, and feel it’s something many people will also love — especially people new to WP and blogging — but we’re getting mixed reactions to just how big it is.
Header image size isn’t a really big deal if you have flexible header heights. To allow maximum customization for Twenty Eleven bloggers that want a smaller header image we’re recommending a core change to allow flexible header heights. It’d benefit more than just the default theme; flexible height headers is a top user request for themes on WP.com.
We’d love your feedback and your help getting it into 3.2.
See https://core.trac.wordpress.org/ticket/17242 for the juicy details.