ConNegModule.cs

namespace NancyConNegDemo
{
    using Extensions;
    using Models;
    using Nancy;

    public class ConNegModule : NancyModule
    {
        public ConNegModule() : base("/conneg")
        {
            Get["/user/{id}"] = x =>
                {
                    var model = database.GetUserById(x.id);

                    return I.RespondTo(ContentType.Html).WithView("UserView")
                            .RespondTo(ContentType.Json)
                            .RespondTo(ContentType.Xml)
                            .UsingModel(model)
                            .CacheFor(7).Days
                            .WithETag(hash);
                };

            Get["/widget/{id}"] = x =>
                {
                    var model = database.GetWidgetById(x.id);

                    return I.RespondToAll()
                            .Except(ContentType.Html)
                            .UsingModel(model);
                };
        }
    }
}

I'm not totally sure. Just thinking outloud, I'd probably rather handle this at the application level based on conventions I want for my application or model. I'm not sure I'd want to repeat all that .RespondTo stuff for every method.