I'd like something like this in future Impact versions:

ig.module(
    'plugins.hitbox'
)
.requires(
    'impact.entity'
)
.defines(function(){

ig.Entity.inject({
    
    hitbox: {
        left: null,
        right: null,
        top: null,
        bottom: null
    },
    
    init: function( x, y, settings ){
        this.parent( x, y, settings );
        if( !this.hitbox.left ){
            this.hitbox = {
                left: x,
                right: x + this.size.x,
                top: y,
                bottom: y + this.size.y
            }
        }
    },
    
    touches: function( other ){
        return !(
			this.hitbox.left > other.hitbox.right ||
			this.hitbox.right < other.hitbox.left ||
			this.hitbox.top > other.hitbox.bottom ||
			this.hitbox.bottom < other.hitbox.top
		);
    },
	
	update: function(){
		this.parent();
		this.hitbox.right -= this.hitbox.left + this.pos.x;
		this.hitbox.left = this.pos.x;
		this.hitbox.bottom -= this.hitbox.top + this.pos.y;
		this.hitbox.top = this.pos.y;
	}

});

});

Added to github for those interested.