Ever frustrated by the fact that the php.ini changes to take effect in your FastCGI setup you need to either flush the current instances or just wait until they die off. You might want to take a look at the latest post from Ruslan Yakushev about the MonitorChangesTo setting that's recently been introduced.
The latest releases of the FastCGI Extensoin 1.5 and FastCGI update for IIS 7.0 have a new configuration setting monitorChangesTo that takes an absolute path to a file that FastCGI will monitor for changes. In case of PHP this means that you can set monitorChangesTo to a path to php.ini file, so that any time it is modified the FastCGI module will restart the php-cgi.exe to pick up the configuration changes.
He includes a few examples of how to use it with different versions of IIS - 5.1/6.0, 7.0 and the latest - 7.5. Configuration settings and screenshots are included as needed.