How to Get Notified when Your Client Installs/Uninstalls a Plugin More: http://club.orbisius.com/howto/wordpress-tips/get-notified-client-installs-uninstalls-wordpress-plugin/

my-spy.php

<?php

/**
 * This file will send you alerts when your clients install/uninstall plugins
 * Usage: Save this as wp-content/mu-plugins/my-spy.php
 * 
 * License: GPL
 * @author orbisius.com
 * Use it at your own risk. You may have to disclose this in your terms of service.
 * Check with a laywer first.
*/
define('SPY_MANAGE_PLUGINS_TO', 'you@yoursite.com');
define('SPY_MANAGE_PLUGINS_FROM', 'Manage Plugins <spy@%host%>'); // use %host% to let the plugin determine the host

add_action('activated_plugin', 'orbisius_my_spy_manage_plugins', 10, 2);
add_action('deactivated_plugin', 'orbisius_my_spy_manage_plugins', 10, 2);

/**
 * This functon is triggered when a plugin is activated or deactivated.
 * It saves the event: activate_plugin, deactivate_plugins.
 * The information is sent to an email defined by SPY_MANAGE_PLUGINS_TO const.
 *
 * @param string $plugin e.g. plugin-dir/plugin.php
 * @param bool $network_deactivating
 * @return void nothing
 */
function orbisius_my_spy_manage_plugins($plugin, $network_act_deactivating) {
    $site = site_url();

    // the last item from the array contains the event: activate_plugins/deactivate_plugins
    $callers = debug_backtrace();
    $caller = array_pop($callers);

	$ip = empty($_SERVER['REMOTE_ADDR']) ? '0.0.0.0' : $_SERVER['REMOTE_ADDR']; // command line scripts won't have IP set.

    $network_act_deactivating = $network_act_deactivating ? 'Y' : 'N';

    $buff = '';
    $buff .= "Site: $site | ";
    $buff .= "Plugin: $plugin | ";
    $buff .= "Method: {$caller['function']} | ";
    $buff .= "network act/deactivating: $network_act_deactivating | ";
    $buff .= "IP: $ip | ";

    $current_user = wp_get_current_user();

    if (!empty($current_user->ID)) {
        $buff .= 'Username: ' . $current_user->user_login . ' | ';
        $buff .= 'User email: ' . $current_user->user_email . ' | ';
        $buff .= 'User first name: ' . $current_user->user_firstname . ' | ';
        $buff .= 'User last name: ' . $current_user->user_lastname . ' | ';
        $buff .= 'User display name: ' . $current_user->display_name . ' | ';
        $buff .= 'User ID: ' . $current_user->ID . ' | ';
    }

    $buff .= "Date: " . date('r');    
    $buff .= "\n";

    $headers = 'From: ' . SPY_MANAGE_PLUGINS_FROM . "\r\n";

    $host = $_SERVER['HTTP_HOST'];
    $headers = preg_replace('#[\%\{]+host[\%}]+#si', $host, $headers);

    // Bon Voyage Email!
	wp_mail(SPY_MANAGE_PLUGINS_TO, 'Manage Plugin: ' . $host, $buff, $headers);
}