By default the header in TwentyTen is not clickable. If you click on it, it does not do anything.
I think this is something that should be activated if possible, because many people click on headers to take them back to the starting page, even if that page is on the menu bar as well.
To do this it is just one line of code that needs to be replaced.
PLEASE BACKUP YOUR THEME BEFORE MAKING THESE CHANGES!
1. Log into the Dashboard using an administrator account.
2. Select “Editor” under “Appearance” in the sidebar.
3. Select “Header (header.php)” in the right-hand column.
4. Search for<div id=”header”>
5. Replace this with <div id=”header” onclick=”location.href='<?php bloginfo(‘url’) ?>’;” style=”cursor: pointer;”>
6. Click on “Update file”.