WP Custom User Meta

gistfile1.php

<?php
/**
 * Add custom user fields/meta info
 */

add_action( 'show_user_profile', 'wu_custom_user_meta', 9 );
add_action( 'edit_user_profile', 'wu_custom_user_meta', 9 );

function wu_custom_user_meta( $user ) {
	// create nonce field
	wp_nonce_field( 'wu_custom_user_meta', 'wu_meta_nonce' );

	?>
	<h3>Custom Section Title</h3>

	<table class="form-table">

		<tr>
			<th><label for="field_name">Field Label</label></th>
			<td>
				<input type="text" name="field_name" id="field_name" value="<?php echo esc_attr( get_the_author_meta( 'field_name', $user->ID ) ); ?>" class="regular-text" />
			</td>
		</tr>


	</table>
<?php }

/**
 * Save custom user fields/meta info
 */

add_action( 'personal_options_update', 'wu_save_custom_user_meta' );
add_action( 'edit_user_profile_update', 'wu_save_custom_user_meta' );

function wu_save_custom_user_meta( $user_id ) {
	// validate permissions
	if ( !current_user_can( 'edit_user', $user_id ) ) {
		return false;
	}

	// verify nonce
	check_admin_referer( 'wu_custom_user_meta', 'wu_meta_nonce' );

	// update fields
	update_usermeta( $user_id, 'field_name', $_POST['field_name'] );
}

Props to this tutorial: http://justintadlock.com/archives/2009/09/10/adding-and-using-custom-user-profile-fields