Using a knight and queen for a discovered check. Usually wins material.

I was playing against my friend and I had a strong position. I had two knights on his 4th rank, ready to attack his king and queen. Behind the d-file knight I had my queen, so that when the knight infront of it moves (and captures a bishop), it reveals a check. After he moved his king, the knight was free to take the queen. The exchange won a queen and a bishop for a knight.

Some people have pointed out that Qh5+ is a better move because it would lead to mate. This is true, but it couldn't be played in this game, because other pieces were preventing it.

This tactic weakened him considerably and quickly lead to checkmate for me.

Is this tactic well-known? Has anyone else found it useful?

Here's a picture of the position. It's the same position as in the game, but with the other pieces removed.

http://i.imgur.com/mrlB8.png

Keep in mind that this is a simplified version of the actual position with unimportant pieces removed. This happened just after the opening, so there were a lot of pieces still on the board and a lot of play to consider. This tactic wasn't as easy to pull off as the diagram makes it seem.

It mostly relied on the fact that he'd delayed his castle too long, and he'd allowed me to put my knights in those strong positions.

I've been noticing discovered checks a lot recently, but this was a particularly strong one. The idea with using a knight infront of a queen (or rook) to discover a check is that once the knight's moved and the king is in check, the knight can take any piece it likes on its next move. If you look ahead for this, you can plan where the knight will be and win material.

Any thoughts on this?

Excellent advice, and a powerful tactic well executed.  I love your illustrations.  I think your last sentence is the key: "If you look ahead for this, you can plan where the knight will be and win material."  Knowing about discovered checks is important, but we have to assume our opponent knows about them too, and won't let us use the tactic against him.  The idea then is to always be on the look out for an opportunity, and to proactively create one; it's much easier to find something if you actively search for it.