According to this blog post: http://www.securityandcaffeine.com/2008/04/03/php-mysql-and-mysql_fetch_array/
mysql_fetch_array() can be sped up dramatically by including quotes, like this:
$result['2'] rather than this $result
I just changed my code to use quotes, and I haven't noticed a big speed increase (that's probably not where the bottleneck is).
Edit: This is probably misleading according to the good people at stackoverflow. http://stackoverflow.com/questions/11345894/mysql-fetch-array-quotes-increase-speed