After updating to WordPress 3.1 I noticed I no longer had page excerpts. In older versions, a plugin was required for pages to have excerpts, but with WordPress 3.0 plugins were no longer required.
With the upgrade to WordPress 3.1, however, I noticed they were missing again, at least in the theme I was using.
The solution was to add this filter to the functions.php file in my theme:
add_post_type_support( ‘page’, ‘excerpt’ );
Now, all is right with the world!