The hearts are a part of the user reputation system. It is mostly covered here
http://zeldadungeon.net/forum/showthread.php?15362-Reputation-System
Basically every post you make can be voted on by other members if they liked it or did not like it. If a post is particularly impressive or funny then someone will add to your user reputation. Or if they thought a post was not contributing to a discussion or saw it to be trollish they will disagree by placing negative reputation. The number of points received or lost can be viewed in your user settings. And when you gain enough points another heart will appear. If you loose too many the heart will be replaced by a skull. And only by gaining more positive reputation points will it be replaced by a heart again. If you gain more hearts then the amount of points you can give goes up.
http://zeldadungeon.net/forum/showthread.php?15362-Reputation-System
Basically every post you make can be voted on by other members if they liked it or did not like it. If a post is particularly impressive or funny then someone will add to your user reputation. Or if they thought a post was not contributing to a discussion or saw it to be trollish they will disagree by placing negative reputation. The number of points received or lost can be viewed in your user settings. And when you gain enough points another heart will appear. If you loose too many the heart will be replaced by a skull. And only by gaining more positive reputation points will it be replaced by a heart again. If you gain more hearts then the amount of points you can give goes up.