Traditions: Beware of Pigs on the Way to the Church
This article elucidates the origins of wedding traditions. There are contradictory explanations and it's not the best organized (or even necessarily true--who knows?) but it's interesting nonetheless, and you can read it to kill time while waiting for the next Harry Potter to come out.
I think that the tying the knot one is the major one they got wrong--from their explanation it sounds like "untying the knot." I always heard it came from handfasting, where the lovers' hands were 'bound' or tied with rope/string to symbolize their bond.
And who knew that while a black cat is perfectly lucky and desirable to see en route on the wedding day, one should avoid pigs and nuns? (The one about avoiding open graves, well, that's pretty intuitive.)
Some hideous marriage history:
The first marriages were by capture, i.e., the groom would kidnap the woman, and take her away from her tribe with the help of a warrior friend, his best man, who would help him fight off other men who wanted this woman, and also help him prevent her family from finding them.
The groom would put himself and his bride into hiding, the honeymoon, and by thetime the bride’s family found them, the bride would already be pregnant. When the groom fought off other warriors who also wanted his bride, he would hold onto her with his left hand, while fighting them off with his sword in his right hand, which is why the bride stands on the left, and the groom on the right.
Although the above was common, marriage by purchase was preferred. Usually the bride would be bartered for land, social status, or political alliances, but sometimes she was exchanged for cash. The Anglo-Saxon word "wedd" meant that the groom would vow to marry the woman, but it also meant the money or barter that the groom paid the bride’s father. A wedding, then, literally meant the purchase of a bride for breeding purposes. The word wedding comes from a root word meaning to gamble or wager.
There were also arranged marriages, where the groom’s family told him who he was to marry, and they very rarely let him see the bride because if he didn’t like her looks, he may refuse to marry her. Therefore, the father of the bride gave the bride away to the groom, who lifted the opaque veil to see her for the first time. This is also the origin of the custom of the bride and groom not seeing each other on the wedding day.