A friend of mine was watching some games on ICC a few days ago, and wanted me to have a look at a completed 3' + 2" blitz game between two GMs. White had a knight and pawn vs. two pawns, and although his pawn was safe and the enemy pawns were blockaded, he was unable to win it. My friend's first thought was that it was an amusing display of GM incompetence (something that's always possible in speed chess, of course), but then I spent a few minutes trying to figure out how to win the ending without getting to the bottom of it either (I did make some progress, though). Admittedly, I wasn't trying my very hardest, but it wasn't a completely trivial effort either.
So have a look and see how you do. It's White to move here (Black has just played 41...Kc4):
You can see for yourself what happened in the game; as for what should have happened, I'll post that in a day or two.