インストールされているPEARパッケージを確認するPHPコードです。

<?php
    require_once 'PEAR/Config.php';
    require_once 'PEAR/Registry.php';
    $config=new PEAR_Config();
    $registry=new PEAR_Registry($config->get('php_dir'));
    $packages=$registry->listPackages();
    echo "<pre>";
    print_r($packages);
    echo "</pre>";
?>

とあるレンタルサーバーで実行してみた結果：

Array
(
    [0] => http_request
    [1] => xml_rpc2
    [2] => xml_rpc
    [3] => console_getargs
    [4] => text_password
    [5] => mail_mime
    [6] => mdb_querytool
    [7] => services_yahoo_jp
    [8] => http
    [9] => html_treemenu
    [10] => ole
    [11] => file_passwd
    [12] => db_querytool
    [13] => db_nestedset
    [14] => html_common
    [15] => services_google
    [16] => html_template_sigma
    [17] => services_yahoo
    [18] => pear_info
    [19] => services_youtube
    [20] => html_quickform_controller
    [21] => soap
    [22] => mail_mimedecode
    [23] => html_common2
    [24] => validate
    [25] => db_ldap
    [26] => net_dime
    [27] => mdb2_driver_mysql
    [28] => file_archive
    [29] => cache_lite
    [30] => mail_queue
    [31] => pear
    [32] => auth_radius
    [33] => auth_sasl
    [34] => mail
    [35] => services_amazon
    [36] => crypt_chap
    [37] => xml_util
    [38] => mime_type
    [39] => date_holidays
    [40] => html_quickform
    [41] => html_menu
    [42] => archive_tar
    [43] => xml_feed_parser
    [44] => spreadsheet_excel_writer
    [45] => net_imap
    [46] => console_getopt
    [47] => date_holidays_japan
    [48] => net_socket
    [49] => services_digg
    [50] => log
    [51] => http_upload
    [52] => mdb2
    [53] => pager
    [54] => mdb
    [55] => mdb2_driver_pgsql
    [56] => services_technorati
    [57] => text_captcha
    [58] => html_ajax
    [59] => http_header
    [60] => php_compat
    [61] => net_useragent_mobile_gps
    [62] => system_command
    [63] => services_opensearch
    [64] => net_useragent_detect
    [65] => db_pager
    [66] => config
    [67] => structures_graph
    [68] => net_smtp
    [69] => net_url
    [70] => auth
    [71] => net_vpopmaild
    [72] => text_figlet
    [73] => db
    [74] => auth_http
    [75] => image_text
    [76] => http_client
    [77] => html_template_it
    [78] => xml_parser
    [79] => xml_tree
    [80] => db_table
    [81] => phpunit
    [82] => text_highlighter
    [83] => xml_rss
    [84] => date
    [85] => db_dataobject
    [86] => net_useragent_mobile
    [87] => http_download
    [88] => net_pop3
    [89] => services_hatena
    [90] => xml_serializer
    [91] => auth_prefmanager
    [92] => mdb2_driver_sqlite
)

結構インストールされてる。