(This picture is of one of my favorite couples -Kiersten & Jason; aren't they both just gorgeous!)
After recently having 2 baby showers of significant sizes, believe me, I understand the (for lack of a better word) Inconvenience of hand writing Thank You cards, but I must tell you, etiquette wise it is an absolute necessity!
Couples often ask me if they "HAVE TO" do it, and while I don't feel anything is mandated, I absolutely feel that if someone takes the time to participate in your special day, the least you can do is thank them for thinking enough of you to share in your joy. You invite these guests because you feel that your day would be a little more complete with their presence, so take the time to WRITE a little note to acknowledge that you and your new spouse appreciate their well wishes (and gifts).
A few things to note when writing your notes...
Be as sincere as possible; If you are going to handwrite your thank you's though a generic message is acceptable, try to put something "special" in the note. While this does not necessarily mean reference the specific gift, you can do little things such as address the guest in their nickname, etc.
If you do not want to handwrite your thank you notes, select a generic message that covers all scenarios. Aside from thanking for the "gift", also thank for well wishes, etc.
Order your thank you notes at the same time as your invitations. In terms of cohesiveness, it's the easiest way to assure that your all of your stationary are the same. There would be nothing worse than waiting 5 months to order a line that possibly has gone out of circulation.
Lastly, be sure to budget $$$ for stamps! Couples often forget to allocate money for the stamps for thank you cards and depending on your guest list size, this may be a significant expense.