"Hold that thought."
Birdhouse is a notepad for Twitter, a place to collect and edit your tweets before you actually put them online. It's designed to sit alongside your favorite iPhone Twitter client as a repository for your more polished one-liners. It's wholly unnecessary for anyone who doesn't care to ever think before they tweet. $4.
More than anything, though, at least for today, it's the app with the most amusing introductory video of all time. For today. (I should have edited that.)

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It's also made in part by Adam Lisagor, who is a comedy sorcerer.
What is the track that plays in the background? I know I've heard it in some other ad before as well...
#2: http://en.wikipedia.org/wiki/Popcorn_(instrumental)
as a fashion guru, I must point out Mr. Lisagor's pants and jacket may not exactly match.