What's the proper etiquette for responding to Facebook wall posts on your birthday? Do you respond to all of them? Write a status update saying "Thanks, pals!" Ignore it completely?
This is the eternal question of our time, second only, perhaps, the one about whether it's really impossible to lick your own elbow. Unless you have 10 friends, the prospect of replying to every single birthday comment can be daunting indeed. You can deal with it a few ways, the best is probably some combination of what you describe in your question.
You should feel free to simply ignore them. Very few people expect a response to a generic online birthday greeting, and really, it's totally fine to not want to "like" or respond to 100 comments that all say some variation of, "Happy birthday!!" (Why is the two exclamation points de rigueur? I don't know. Just do it.) If you have a manageable amount of birthday wishes -- and what's manageable will vary by your dexterity, stamina, and guilt that's induced by a religious upbringing -- you could always go through and "like" each comment, but really, it's not required. It is your birthday, after all. Why should you waste your precious day responding to Facebook comments? You're old now, for God's sake. Go knit a caftan, drink some spiked Metamucil, and ponder the crippling loneliness and pain of your continued existence.
The umbrella thank-you status update is great because it easily allows you to recognize those thoughtful friends who gave you that extra exclamation point and wished you a great day. This is both genuine and desperate-in-a-way-only-you-will-know, because it also gives lazy friends who may not have seen that it's your birthday a second chance to lavish you with sweet Internet validation.
If someone has gone above and beyond the generic, or if they are actually a good friend, it's nice to give that person a little bit of attention, whether in comment form or private message. Think of the generic comment as the friend-equivalent of dining in an Olive Garden. Yes, you appreciate the unlimited breadsticks and iceberg lettuce, but such gestures alone don't compel you to lavishly tip. Nor should they, especially because you know you're going to get some kind of intestinal virus later. If a friend takes the time to post a photo of the two of you, or an inside joke, or that delightful Justin Bieber video where he sings happy birthday to an empty stadium for the American Cancer Society, then that deserves a response.
Social-media mistress Anna Pulley likes to give advice about how to play well with others on the internets. If you have a question about etiquette involving technology, shoot her a question at AskAnnaSF@gmail.com.