A lot of solutions written in PHP use PEAR components - so you might be using PEAR as a consumer already.

phpMyAdmin: Spreadsheet_Excel_Writer and PEAR_SOAP

MediaWiki: Text_Diff

eGroupWare: HTTP_WebDAV, Net_IMAP

Gallery2: HTML_Safe, Mail_Mime

Magento uses PEAR to update the system and manage plugins

Symfony does similar

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