Why do celebrities use Twitter? To be honest, it's pretty easy to answer that... Just think about it, and you're probably right.

However, it's nice to hear them talk about the social networking service in their own words, and this video puff piece - filmed to celebrate its fifth birthday - is crammed with names: Virgin supremo Richard Branson (@RichardBranson), Snoop Dogg (@SnoopDogg), Hilary Clinton (@StateDept), Serena Williams (@serenawilliams), Julian Perretta (@julianperretta), Martha Stewart (@MarthaStewart) and more reveal their Twitter habits. Oh, and Piers Morgan (@piersmorgan)... But you can always skip past that bit.

But the best bit to watch this clip is to see the view that astronaut Paolo Nespoli (@astro_paolo) wakes up to every day... Breathtaking.