WCF ChannelFactory and Channel caching in ASP.NET client application

I'm building a series of WCF Services that are going to be used by more than one application. Because of that I'm trying to define a common library to access WCF services.

Knowing that each service request made by different users should use a different Channel I'm thinking in cache the Channel per-request (HttpContext.Current.Items) and cache the ChannelFactory used to create the channel per Application (HttpApplication.Items) since I can create more than one channel with the same ChannelFactory.

However, I have a question regarding this cache mechanism when it comes to closing the ChannelFactory and Channel.

1. Do I need to close the Channel after it's used, at the end of the request, or is it ok to leave it there to be closed (?) when the context of that request dies?
2. What about ChannelFactory? Since each channel is associated with the ChannelFactory that created it, is it safe to keep the same ChannelFactory during the life of the application process (AppDomain)?

This is the code I'm using to manage this:

public class ServiceFactory
{
    private static Dictionary<string, object> ListOfOpenedChannels
    {
        get
        {
            if (null == HttpContext.Current.Items[HttpContext.Current.Session.SessionID + "_ListOfOpenedChannels"])
            {
                HttpContext.Current.Items[HttpContext.Current.Session.SessionID + "_ListOfOpenedChannels"] = new Dictionary<string, object>();
            }

            return (Dictionary<string, object>)HttpContext.Current.Items[HttpContext.Current.Session.SessionID + "_ListOfOpenedChannels"];
        }
        set
        {
            HttpContext.Current.Items[HttpContext.Current.Session.SessionID + "_ListOfOpenedChannels"] = value;
        }
    }

    public static T CreateServiceChannel<T>()
    {
        string key = typeof(T).Name;

        if (ListOfOpenedChannels.ContainsKey(key))
        {
            return (T)ListOfOpenedChannels[key];
        }
        else
        {
            ChannelFactory<T> channelF = new ChannelFactory<T>("IUsuarioService");
            T channel = channelF.CreateChannel();
            ListOfOpenedChannels.Add(key, channel);
            return channel;
        }
    }
}

Thanks!

Ideally close the channel as soon as you are done with it. This will place it back into the channel pool so it can be used by another worker thread.

Yes, the channel factory (the expensive bit) can remain for the lifetime of the application.

Update

As of .Net 4.5 there is a built in caching options for factories ChannelFactory Caching .NET 4.5