To make sure I got your request right, you want the number of user urls displayed to be random, or rather the selection of those urls?
Don’t know of a plugin, but displaying random (but a fixed number of) user urls is a somewhat simple bit of code:
<ul>
<?php
global $wpdb;
$limit_urls = 10; // set to # of urls to display
$randusers = $wpdb->get_results("SELECT * FROM $wpdb->users ORDER BY RAND() LIMIT $limit_urls");
foreach($randusers as $user) :
$linkname = ($user->display_name) ? $user->display_name : $user->user_login;
?>
<li><a href="<?php echo $user->user_url; ?>"><?php echo $linkname; ?></a></li>
<?php endforeach; ?>
</ul>
Change the $limit_urls value to set the number of links to display. Note that $linkname tests whether a display name has been set (if not, login name is used).
For a random number of urls, change the $limit_urls line to:
$limit_urls = mt_rand(0, $wpdb->get_var("SELECT COUNT(ID) FROM $wpdb->users"));
This generates a random number with the max (highest number) argument seeded by a count of the user IDs.
