/*
 * Localized default methods for the jQuery validation plugin.
 * Locale: RU
 */
jQuery.extend(jQuery.validator.methods, {
    date: function (value, element) {
        return this.optional(element) ||

            /^([1-2][0-9]|0?[1-9]|3[0-1])(\.(0?[1-9]|1[0-2])(\.([1-2]\d{3}|\d{2}))?)?(\s(2[0-3]|[0-1]?\d)(:[0-5]?\d){1,2})?$/.test(value)

            ||

            /^(2[0-3]|[0-1]?\d)(:[0-5]?\d){1,2}$/.test(value);
    }
    ,
    number: function (value, element) {
        return this.optional(element) || /^-?(?:\d+|\d{1,3}(?:[\s\.,]\d{3})+)(?:[\.,]\d+)?$/.test(value);
    }
});

<system.web>
    <globalization uiCulture="ru-RU" culture="ru-RU" />
    ...

public class DecimalModelBinder : DefaultModelBinder
{
    public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        object result = null;

        string modelName = bindingContext.ModelName;
        string attemptedValue = bindingContext.ValueProvider.GetValue(modelName).AttemptedValue;

        string wantedSeperator = NumberFormatInfo.CurrentInfo.NumberDecimalSeparator;
        string alternateSeperator = (wantedSeperator == "," ? "." : ",");

        if (attemptedValue.IndexOf(wantedSeperator) == -1
            && attemptedValue.IndexOf(alternateSeperator) != -1)
        {
            attemptedValue = attemptedValue.Replace(alternateSeperator, wantedSeperator);
        }

        try
        {
            result = decimal.Parse(attemptedValue, NumberStyles.Any);
        }
        catch (FormatException e)
        {
            bindingContext.ModelState.AddModelError(modelName, e);
        }

        return result;
    }
}

ModelBinders.Binders.Add(typeof(decimal), new DecimalModelBinder());
ModelBinders.Binders.Add(typeof(decimal?), new DecimalModelBinder());