Extending STSADM Command set

Scenario:
You want to extend STSADM by including a new operation for enumerating all the features for a given site.

Code(GAC):

using System;
using System.Collections.Specialized;
using System.Text;
using Microsoft.SharePoint;
using Microsoft.SharePoint.StsAdmin;

namespace TrainingSamples
{
    public class SimpleCommandHandler : ISPStsadmCommand
    {
        public string GetHelpMessage(string command)
        {
            return "-url <full url to a site in SharePoint>";
        }

        public int Run(string command, StringDictionary keyValues, out string output)
        {
            command = command.ToLowerInvariant();

            switch (command)
            {
                case "enumfeatures":
                    return this.EnumerateFeatures(keyValues, out output);

                default:
                    throw new InvalidOperationException();
            }
        }

        private int EnumerateFeatures(StringDictionary keyValues, out string output)
        {
            if (!keyValues.ContainsKey("url"))
            {
                throw new InvalidOperationException("The url parameter was not specified.");
            }

            String url = keyValues["url"];

            SPFeatureCollection features = null;
            SPWeb web = null;

            try
            {
                SPSite site = new SPSite(url);

                web = site.OpenWeb();

                features = web.Features;
            }
            catch (Exception e)
            {
                throw new InvalidOperationException("Error retrieving url '" + url + "'.  Please check the format of your url, and ensure that the site exists.  Details: " + e.Message);
            }

            StringBuilder sb = new StringBuilder();

            sb.AppendLine("Features at '" + web.Url + "':\n");

            foreach (SPFeature feature in features)
            {
                sb.AppendLine(feature.Definition.DisplayName + " (" + feature.DefinitionId + ")");
            }
        
            output = sb.ToString();

            return 0;
        }
    }
}

STSADMCommands.TrainingSamples.xml(12\Config):

<?xml version="1.0" encoding="utf-8" ?>

<commands>
    <command
      name="enumfeatures"
      class="TrainingSamples.SimpleCommandHandler, [full 4-part assembly name]"/>
</commands>

Usage:

stsadm -o enumfeatures -url http://localhost