Customer Support

Using ini_set("include_path"... is particularly useful if you want to
use something like PEAR, but your hosting provider does not have all the
packages installed that you want to take advantage of.  eg.  My hosting
provider does not include the SOAP package, so I just add the package
into a directory in my web space, and then add that directory to my
include path.

Setting include path also helps to make keep your servers clear of
duplicates if you use the same libraries for different projects on the
same server. Just put the library (for example ADOdb is a popular
database abstraction library) into a central folder and you can use it
in multiple projects without having to worry about directory structure.

Include_path errors suspected as configuration errors might be errors in
php scripts run on a new installation. If scripted path errors ran on an
installation that didn't report warnings then ran on an installation
that does report warnings, the error might first be noticed on a new PHP
installation.

I chased a posited config error that wasn't there until I realized the
warnings that showed up on several pages related to code instead of
configuration. Multiple errors in scripts on a new installation didn't
show on the old server, and seemed to me to result from one cause until
I cleaned up paths, missing files and broken function calls that all
return warnings on the new installation.

Several online PHP installation error reports reference
(include_path='.;C:\php5\pear'). Be sure a wrong relative path in a php
script isn't the cause.

To add a path to the already existing value (not just replace) do
something like this:

ini_set('include_path', 
  ini_get('include_path') . PATH_SEPARATOR . '/path/to/add')