I have just found a problem with this mod, Using 6.6.1 on a raq550 and "i386-redhat-linux-gnu"
The ultimatebb.cgi part of the hack ads "ubb->ultimatebb.cgi" to the $in hash when there is no options in the url. This cause 2 problems.
The first was it would not display the forum summary because it could not get a blank "ubb" key - I fixed this by adding in the old section from my older 6.3 version.
But the second problem caused the forum summary to only display the default html template - this was caused by the "&DetermineDefaultTemplates($in{ubb})" sub failing to return "summary_page" again due to the $in{ubb} containing "ultimatebb.cgi".
While i just typed that i realised that its because i have my cgi path set to ubb so anyone who dosnt have it set up like that wont have this problem.
Anyway i fixed it with "if ($in{"ubb"} eq "ultimatebb.cgi") {delete $in{"ubb"}};" but it is not checked for case so it may need tweaking for others who have this problem. (if there are any :s)