Ok, so I enclosed my App::make() in var_dump() and got a response:

class Project\Frontend\Repo\Lead\EloquentLead#798 (1) {
  protected $lead =>
  class Lead#809 (21) {
    // bunch of info about the model etc relating to the interface and it's repo class
  }
}

One of the members in #laravel pointed out that this meant the interface was instantiated which is great but then I realised this isn't the interface that I'm having a problem with. So below is how I have things setup. The interface that's apparently not instantiated is ValidableInterface (last portion of code) and running var_dump(App::make()) for this interface returns the dreaded "Target not instantiated" error. Am I missing some glaring problem with my code?

My service provider

<?php namespace Project\Frontend\Service\Form;

use Illuminate\Support\ServiceProvider;
use Project\Frontend\Service\Form\Lead\LeadForm;
use Project\Frontend\Service\Form\Lead\LeadFormLaravelValidator;

class FormServiceProvider extends ServiceProvider {

    /**
     * Register the binding
     *
     * @return void
     */
    public function register()
    {
        $app = $this->app;

        $app->bind('Project\Frontend\Service\Form\Lead\LeadForm', function($app)
        {
            return new LeadForm(
                new LeadFormLaravelValidator( $app['validator'] ),
                $app->make('Project\Frontend\Repo\Lead\LeadInterface')
            );
        });
    }

}

My form class

<?php namespace Project\Frontend\Service\Form\Lead;

use Project\Backend\Service\Validation\ValidableInterface;
use Project\Frontend\Repo\Lead\LeadInterface;

class LeadForm {

    /**
     * Form Data
     *
     * @var array
     */
    protected $data;

    /**
     * Validator
     *
     * @var \Project\Backend\Service\Validation\ValidableInterface
     */
    protected $validator;

    /**
     * Lead repository
     *
     * @var \Project\Frontend\Repo\Lead\LeadInterface
     */
    protected $lead;

    public function __construct(ValidableInterface $validator, LeadInterface $lead)
    {
        $this->validator = $validator;
        $this->lead = $lead;
    }

My validation rules

<?php namespace Project\Frontend\Service\Form\Lead;

use Project\Backend\Service\Validation\AbstractLaravelValidator;

class LeadFormLaravelValidator extends AbstractLaravelValidator {

    /**
     * Validation rules
     *
     * @var Array
     */
    protected $rules = array(
        'name' 				=> 'required|regex:/^[a-zA-Z-\s]+$/',
        'email' 			=> 'email',
        'cell' 				=> 'required|numeric|digits_between:10,11',
    );

    /**
     * Validation messages
     *
     * @var Array
     */
    protected $messages = array(
		'regex' 				=> 'The :attribute may only contain letters, dashes and spaces.',
		'digits_between' 		=> 'The :attribute must be 10 numbers long.',
	);

}

My abstract validator

<?php namespace Project\Backend\Service\Validation;

use Illuminate\Validation\Factory;

abstract class AbstractLaravelValidator implements ValidableInterface {

    /**
     * Validator
     *
     * @var \Illuminate\Validation\Factory
     */
    protected $validator;

    /**
     * Validation data key => value array
     *
     * @var Array
     */
    protected $data = array();

    /**
     * Validation errors
     *
     * @var Array
     */
    protected $errors = array();

    /**
     * Validation rules
     *
     * @var Array
     */
    protected $rules = array();

    /**
     * Custom validation messages
     *
     * @var Array
     */
    protected $messages = array();

    public function __construct(Factory $validator)
    {
        $this->validator = $validator;
    }

    /**
     * Set data to validate
     *
     * @return \Project\Backend\Service\Validation\AbstractLaravelValidator
     */
    public function with(array $data)
    {
        $this->data = $data;

        return $this;
    }

    /**
     * Validation passes or fails
     *
     * @return Boolean
     */
    public function passes()
    {
        $validator = $this->validator->make($this->data, $this->rules, $this->messages);

        if( $validator->fails() )
        {
            $this->errors = $validator->messages();
            return false;
        }

        return true;
    }

    /**
     * Return errors, if any
     *
     * @return array
     */
    public function errors()
    {
        return $this->errors;
    }

}

My validator interface

<?php namespace Project\Backend\Service\Validation;

interface ValidableInterface {

    /**
     * Add data to validation against
     *
     * @param array
     * @return \Project\Backend\Service\Validation\ValidableInterface  $this
     */
    public function with(array $input);

    /**
     * Test if validation passes
     *
     * @return boolean
     */
    public function passes();

    /**
     * Retrieve validation errors
     *
     * @return array
     */
    public function errors();

}