White's N maneuvers are instructive.

I think many people would have been trying to hold on to the passed b pawn. My guess is that Smyslov decided that pawn would fall and he might as well convert to a modest material advantage.

So what was black's mistake? My guess is 36...fxg4, followed by 37...Bd3. If he had played 36...h6 and maintained the pawn at f5, white would not have broken through.>

Although I substantially disagree, I think this is an excellent comment because it is very thought–provoking. I would offer these observations: (1) After move 30, the position looks to me to be one in which White does not yet have a won game, but does have good winning chances primarily due to the superiority of his Bishop and White’s better prospects to activate his King utilizing Black’s weakness on the central dark squares; (2) Accordingly, it made perfect sense for White to continue playing (and would have done so even if the two opponents had been of a class comparable to one another); (3) if the position after move 30 had arisen, for example, in a game between Kramnik and Leko and been agreed drawn at that point, the kibitzers with howls of protest about "Drawnik" and "Drawko" would have been legion; and (4) finally and obviously, Smyslov had every reason to expect he would have good chances decisively to outplay a “mere” 2300 player in an endgame (even if the position at move 30 had been equal).

At first I thought 15...Ng4 was a trap, but
after 15...Ng4 16 h3 Nxe3 17 fxe3 Qxe6 18 cxd5 gives back the initiative to White.

click for larger view

Back to the game, I would go as far as to say whether this game is a black or white win has nothing to do with move 30. I think black made a horrible error on 19! For the simple reason as has been mentioned before: In a single move he puts yet another pawn on the same colour, and gives up the bishop thats on the opposite colour to his pawns. In endgames especially, it is easy to go as far as saying thing type of thing is suicide! Black's bishop can't attack white's pawns, whereas White's bishop can attack his. Therefore He will always have a weak, continually defending bishop and white will always have a strong, mobile one. As of move 43 for example, the ONLY thing the Black bishop can actually attack is White's bishop! Now you can see how this stupid decision at move 19 wrecks his game 24 moves later.

So now he only has one effective piece on the board (the knight), unfortunately that is forced to defend (from the back of the board!)as well, and black is well and truly stuffed.

So you see how this is a very instructive game on how bishops interact in a locked-pawn game, and try to apply this in your games, e.g Try to trade off your 'bad bishop' (same colour as your pawns, has to defend, and is blocked in by his own pawns) and keep your 'good bishop' (can attack opponents pawns and move freely around his own pawns), and also try to trade off your opponents good bishop and keep his bad one.