I like the extnesibility point of MVC, allowing view models to implement IValidatableObject, and add custom validation.

I try to keep my Controllers lean, having this code be the only validation logic:

if (!ModelState.IsValid)
    return View(loginViewModel);

For example a login view model implements IValidatableObject, gets ILoginValidator object via constructor injection:

public interface ILoginValidator
{
    bool UserExists(string email);
    bool IsLoginValid(string userName, string password);
}

It seems that Ninject, injecting instances in view models isn't really a common practice, may be even an anti-pattern?

Is this a good approach? Is there a better one?