EDIT: I made something much better to fill and read data from a view using ViewModels, called it ValueInjecter. http://valueinjecter.codeplex.com/documentation

using the ViewModel to store the mapping logic was not such a good idea because there was repetition and SRP violation, but now with the ValueInjecter I have clean ViewModels and dry mapping code

this pattern is usefull when you have to make a form for editing an entity and you have to put on the form some dropdowns for the user to choose some values

public class OrganisationViewModel
{

    //paramterless constructor required, cuz we are gonna get an OrganisationViewModel object from the form in the post save method
    public OrganisationViewModel() : this(new Organisation()) {}

    public OrganisationViewModel(Organisation o)
    {
        Organisation = o;
        Country = new SelectList(LookupFacade.Country.GetAll(), "ID", "Description", CountryKey);  
    }       
    //that's the Type for whom i create the viewmodel
    public Organisation Organisation { get; set; }

    #region DropDowns
    //for each dropdown i have a int? Key that stores the selected value
    public IEnumerable<SelectListItem> Country { get; set; }

    public int? CountryKey
    {
        get
        {
            if (Organisation.Country != null)
            {
                return Organisation.Country.ID;
            }
            return null;
        }
        set
        {
            if (value.HasValue)
            {
                Organisation.Country = LookupFacade.Country.Get(value.Value);
            }
        }
    } 

    #endregion      

}

and that's how i use it

 public ViewResult Edit(int id)
    {            
        var model = new OrganisationViewModel(organisationRepository.Get(id));
        return View(model);
    }

    [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Edit(OrganisationViewModel model)
    {
        organisationRepository.SaveOrUpdate(model.Organisation);
        return RedirectToAction("Index");
    }

and the markup

<p>
            <label for="Name">
                Name:</label>
            <%= Html.Hidden("Organisation.ID", Model.Organisation.ID)%>
            <%= Html.TextBox("Organisation.Name", Model.Organisation.Name)%>
            <%= Html.ValidationMessage("Organisation.Name", "*")%>
        </p>
        <p>
      ...
            <label for="CountryKey">
                Country:</label>
            <%= Html.DropDownList("CountryKey", Model.Country, "please select") %>
            <%= Html.ValidationMessage("CountryKey", "*") %>
        </p>

so tell me what you think about it