You should send out thank you cards within one month of receiving a gift. Each note should be personalized and should express how thankful you are for the gift you received. Since most gifts are opened after the wedding, your thank you note will reassure your guest that you received it.
If you receive a monetary gift, you should let them know how you're planning on spending their generous gift (such as part of a house down payment, new furniture, etc.). Add a little humor and loving sentiment to the card - don't worry about it not being the work of a writer!
The gifts were given to both the bride and groom. Therefore, both of you should write the thank you notes. Have the bride write notes for her family and friends and have the groom write them for his family and friends. If the numbers are uneven, split them up evenly. If you each sit down and write a few a night, you can have them signed, sealed and delivered to go before the month is up! Sit back and have fun with it - don't make it a chore. Enjoy your favorite music and a hot cup of tea while you're writing your thank you notes!