Vinícius Lira over in this comments thread has proposed a ridiculously elegant solution to using a default WordPress installation to host multiple blogs on different databases. If it works, it's genius.

STEP ONE: Create a subdomain that points to your WordPress installation, such as "http://newblog.site.com/"

STEP TWO: Create a new database, such as "newblog"

STEP THREE: Edit the "wp-config.php" file and replace:

define('DB_NAME', 'wordpress');

with:

if($SERVER['HTTPHOST'] == "site.com" or
$SERVER['HTTPHOST'] == "www.site.com") {
  define('DBNAME', 'mysitedatabase');}
elseif ($SERVER['HTTPHOST'] == "newblog.site.com") {
define('DBNAME', 'newblog');
}

Haven't tested it myself yet, but it seems too simple. It shouldn't work. If it does, it'd be schweet.