I just installed this hack yesterday and it slowed my forum (with over 500,000 messages) down to a crawl. Deleting or moving threads became completely impossible. I had a look at their code and found some code that was a bit (without trying to belittle the efforts of the original coder) not-so-efficient programming.
In my case which so many messages, it took about 20 minutes to close/move/delete a thread, causing the browser to time out and the cgi-script to fail. I've made a few changes that brought this 20 minutes down to 0.6 seconds (yes, less than a second).
Since this is an old hack, and I'm not sure anyone is still using it, let me know if you're interested in the fix and I'll post it here.
