If you want to let users have an unlimited list of links, rather than creating many link fields, just use a free-form list field and use this code in your user-profile.tpl.php.

<?php
    $links = explode("\n", trim(_filter_url(str_replace(',', "\n",$account->profile_yourlinksfieldname), 1)));
    print theme('item_list', $links);
?>

This snippet lets you use commas and/or line breaks to separate the links. It will shorten the url to the length set in the filter format you choose. In this case, the 1 in the first line tells _filter_url() to use the default format.

The second line themes the links as a list.

This also works for ftp, mailto, file, etc. as specified in _filter_url().

See:
_filter_url()
theme_item_list()