There probably aren't many people who need this at the moment, but if there is someone out there who has recently moved from the perl to the php version this might be useful. Links in messages written with the perl version will be broken when reading in the PHP version, but this is a quick way to fix it, providing that your Apache server has mod_rewrite installed.
Create a file called ".htaccess" (without the quotes) in the threads directory, and put these lines in it:
RewriteEngine On
RewriteBase /
RewriteRule ^([^\?]+)\.pl(.*)$ $1.php$2 [R,L]
If your installation of threads isn't at the root level of your domain, you will need to change the RewriteBase. Here at threadsdev, it would probably be like this:
RewriteBase /threads/php/