Check out the new free service, FutureTweets:

FutureTweets.com is a free service that lets you schedule your Twitter messages. Send it at a specific time in the future or send a reoccuring Tweet daily, weekly, monthly or yearly!

You'll never forget the birthdays of your beloved Twitter friends again! Just schedule a nice Tweet on their birthday!

Pretty cool huh?

(Oh, and just about every productivity book you can find advocates doing similar type tasks all at once.)