As with everything else in life, we can glean valuable lessons about wedding planning from Seinfeld. Remember what happened when George picked out the envelopes? They were so cheap, so pathetic, that Susan licked the adhesive...and died.
You can learn from Costanza. Remember that episode where he did “The Opposite” of his instincts, reasoning that if every instinct is wrong, the opposite must be right? This is your move. We think it’s unlikely that you will accidentally murder your fiancée, but when it comes to the dreaded Thank You notes just do "The Opposite" of George’s instincts.
George would: Insist on picking out the envelopes.
The Opposite: Get whatever the hell she wants. Who cares, right? By now, you should be familiar with this overarching theme of The Plunge: you need to pick your battles. This is the wrong war at the wrong time for the wrong reasons. Just get whatever Susan wants. Don’t make this your Bay of Pigs.

George would: Write something like, “Thank you for the $15 gift card. I’ll use it to pay for half the dinner that you ate.”
The Opposite: Never mention specific dollars. Even if they actually gave you cash, just tactfully say “generous gift,” not a hard dollar amount. Even if it’s not generous, use the word generous. It’s like telling an old hag that she looks nice: a benevolent lie. If they did give you cash, tell them what you’re using it for: “We’re saving up to convert the basement into a gimp dungeon... we’ll be sure to let you come over and watch!”
George would: Wait a week to write them, then two weeks, then six weeks, then six months, then say “To hell with it Jerry, I got nothin’. I’m empty. I got nothin’. Nothin’!” and then blow the whole thing off.
The Opposite: Knock them out early. However, unlike what the wedding-porn suggests, we do not recommend that you deal with them every day. That’s like mowing one tiny section of your lawn every evening. Just hold your nose, grab a beer, and do a big awful batch once every two weeks while watching Monday Night Football.
George would: Try and dump them all on Susan.
The Opposite: It can’t be done. Every guy’s tried it. Every guy’s failed. The thank you notes, tragically, are a gruesome duty that you must split down the middle. And it gets worse: often she will cutely suggest that she writes to your friends, you write to her friends. Ahhwwwww. Just roll with it. This isn’t fun, but neither is paying taxes. You pay taxes to live in a civilization that has roads and a military; you write thank you notes to live in a marriage that has sex and stability.
George would: Forget what someone gave him...then guess what it was...and guess wrong.
The Opposite: On the spreadsheet you used for your guest list and invitations, insert a column for “Gifts.” Use this to stay organized. You have this spreadsheet, right?
George would: Send an e-mail.
The Opposite: George would send an e-mail to all of his guests (not even giving them the courtesy of a Bcc) with a generic “Thanks for the gifts. Please send any anniversary presents to Vandelay Industries, c/o George...” The man has a point. In an age of global warming and energy crises, why kill more trees to send more letters? Sadly, the fickle laws of decorum dictate that you must write these suckers by hand.

George would: Plagiarize.
The Opposite: Actually, don’t do the opposite. In this case George would be right. While we frequently give them hell, the good folks at About.com have a pretty solid list of sample Thank You notes. Steal from it. Then, when possible, sprinkle in something personal from the ceremony. (i.e. “I’m glad you had a good time sucking face with my cousin. Fat girls need lovin’ too!”)
And that’s that. There’s no magic secret to thank you notes. They’re just a pain in the ass.
For more on what could happen after the wedding, learn about Post-Wedding-Funk.