Eben Upton's reboot of the spirit of the BBC Micro in the form of the Raspberry Pi would have been an interesting project even if it had only been useful in the world of education. Upton wanted, after all, to give the kind of hands-on, low-level interaction with computing devices that he saw had gone missing in schools. Plenty of rPis are now in that educational, inspirational role, but it turns out that the world was waiting (or at least ready) for a readily usable, cheap, all-in-one computer, and the Raspberry Pi arrived near the front of a wave that now includes many other options. Sales boomed, and we've mentioned a few of the interesting milestones, like the millionth unit made in the UK and the two-millionth unit overall. Now, according to TechCrunch the Raspberry Pi is getting close to 4 million units sold, having just passed 3.8 million, as reported in a tweet. If you have a Raspberry Pi, what are you using it for now, and what would you like to see tweaked in future versions?