Thanks to "over-achieving" in Europe and (we'd imagine) a few sales in North America over the holidays, the 360 has reached 28 million units sold worldwide. That's more than 8 million ahead of PS3 and around 12 million (estimated) behind Wii. Microsoft also claims there are around 17 million users on Xbox Live, with over $1 billion in sales occurring on the service.
To give some perspective to these numbers: If you were to stack all the 360s on top of each other, then stack all the PS3s and Wiis next to them, then stack all the PCs and DSs and PSPs in yet another stack and then just walk away, we could probably all get a lot more reading done.