Mmmh, hot! This is one of the reasons I love threesomes - the added character dynamics, the imbalance of power, the sheer hotness of it :).
I loved seeing this from Draco's perspective, who was beautifully in character (and the way he gets off on being fucked by Harry just because it's *Harry* was great fun - and very characteristic). And I adored your Neville - a wonderful mix of pre-DH and DH characteristics, and he really came to life as a personality. And oh, did I mention hot? I liked the negotiations between them (especially Draco's mercenary Slytherin attitude) and the way Harry and Neville get swept along with it :).