OK, just had to mess around with the new default theme for WordPress 3.0 — picked a seasonal image from my photo stash and cropped it to the header image. Picked a second image to make the featured image of this post.
Only downside seems to be that you have to redo widgets with theme changes.
Click the heading of this post if you are in the home page list to see the custom header image (country road vs. daisy).