Another great use of a pawn is in the endgame.  When you and your opponent are even in material, often you can march a pawn down the board to promote it, in effect forcing your opponent to trade a rook or bishop (for example) for that pawn, giving you the advantage.  A passed pawn is a pawn that has no enemy pawns in front of it.  An isolated pawn is a pawn that doesn't have any enemy pawns that can capture it.  Isolated passed pawns can be quite valuable in the endgame, so keep this in mind during the earlier game when you may be tempted to think "it's just a pawn," or it may come back to haunt you.

Another problem a lot of players have is that they are too willing to push many of their pawns out into the middle of the board.  Since pawns cannot move backwards, keep in mind when you want to push a pawn (such as, to threaten your opponent's bishop and get it out of your face, which happens quite often in the first few moves of the game) that the squares beside and behind it are now weakened, as that pawn can never cover those squares again.  Once you have done that, when your opponent gets pieces past those pawns, you will not be able to push him away so easily, and chances are that entire pawn chain will fall.