I had my ASP.NET MVC actions written like this:
    //
    // GET: /TaxStatements/CalculateTax/{prettyId}
    public ActionResult CalculateTax(int prettyId)
    {
        if (prettyId == 0)
            return Json(true, JsonRequestBehavior.AllowGet);
        TaxStatement selected = _repository.Load(prettyId);
        return Json(selected.calculateTax, JsonRequestBehavior.AllowGet); // calculateTax is of type bool
    }
I had problems with this because when using it in jquery functions I had all sorts of error, mostly toLowerCase() function failing.
So I had to change the actions in a way that they return bool as string (calling ToString() on bool values), so that thay return "true" or "false" (in the qoutes) but I kinda don't like.
How others handle such a case?