1. Haven’t looked into that yet, but it should definitely be nofollowed no matter how the link is formatted so this might be worth looking into/filing a trac for.
2. You run the risk of people spamming through their profile if they figure that out, but if you’re willing to take the risk, it’s not too difficult. Open up your templates profile.php, and add the following at the top of the page;
<?php $GLOBALS['bb_nofollow_off'] = TRUE; ?>
…then open bb-includes/backpress/functions.formatting.php and go to line 950 at the bottom of function _make_url_clickable_cb() and replace;
return $matches . "<a href="$url" rel="nofollow">$url</a>";
return (isset($GLOBALS['bb_nofollow_off'])) ? $matches . "<a href="$url">$url</a>" : $matches . "<a href="$url" rel="nofollow">$url</a>";
Note that if you have deep integration, you’ll have to change the above line in your WordPress version of the same function, not the bbPress one.