Anyone who has tried installing XDebug, to help debug PHP, will attest to the fact that it's it not the simplest task in the world.
That may be a little harsh, the actual installation is quite simple, it's the chosing of the correct file to download thats confusing. When downloading the file you need to make sure that all of the following matches (especially for a windows installation):
You then need to update your PHP.ini file.
If you get anything wrong there are no helpful error messages, XDebug just doesn't work. It's like XDebug has not been installed.
Wish I had found this earlier...
Derek Rethans has created a wizard which accepts the output from the phpinfo() function and then gives you the steps for installing XDebug. These steps include the correct file to download, with a link!!!
It's a fantastic tool, which eleminates a lot of heartache.