Two knights and a king vs a king is a draw. Two bishops and a king vs a king is a win. A bishop a knight and a king vs a king is a win (but you have to know the technique, it takes about 50 moves from ideal position (for person being checkmated) to the checkmate.
First of all, it is possible to checkmate with two knights, but basically it's considered a draw because the oponent would have to blunder to allow you to do it (go right into the corner at the wrong time basically).
Secondly, bishop plus knight plus king vs king does not take 50 moves!! That would basically be a draw situation as well if it did! It can be done in less than 30 moves with a good starting situation and the oponent defending perfectly. Much less if the oponent tries to be 'stubborn' - he will only loose faster.
I know because I've practiced this basic checkmate so many times, I've been fascinated by it, constantly trying to improve my efficiency is possible.
I recommend trying the endgame simulator at chessvideos.tv - makes for perfect practice on this one.
can one be easily checkmated with 2 knights, when the opponent has nothing other than the king itself? what do you think? have you ever tried this puzzle?