Two simple methods for ClickOnce deployed applications.

public static class ClickOnce
{
    /// <summary>
    /// Determines whether this instance is deployed.
    /// </summary>
    /// <returns>
    ///     <c>true</c> if this instance is deployed; otherwise, <c>false</c>.
    /// </returns>
    public static bool IsDeployed()
    {
        return (AppDomain.CurrentDomain.ActivationContext != null && ApplicationDeployment.IsNetworkDeployed);
    }

    /// <summary>
    /// Parses the query string.
    /// </summary>
    /// <returns><see cref="NameValueCollection"/> containing the key/value pairs from the ActivationUri if they are found; otheriwise an empty <see cref="NameValueCollection"/>.</returns>
    public static NameValueCollection ParseQueryString()
    {
        if (!IsDeployed())
            return new NameValueCollection();

        Uri uri = ApplicationDeployment.CurrentDeployment.ActivationUri;
        if (uri != null)
        {
            NameValueCollection parms = HttpUtility.ParseQueryString(uri.Query);
            if (parms.Count != 0)
                return parms;
        }

        return new NameValueCollection();
    }
}