IGN has a great piece up right now called "Everything you wanted to know about Xbox 2." They've done an excellent job of combining a lot of information, culled from a lot of sources, into a very readable and jargon-free analysis. But, one part really jumped out at me: Three controller slots? Here's what IGN had to say:
"There are three controller slots, two controllers on front of the system, plus one USB on the back."
Later they claim that the system will be backwards-compatible if the optional hard drive is purchased. Well, if it's going to be backwards compatible, it better have four controller slots. Not only that, but I don't see why four player games wouldn't be important in the next generation, even with Live.
Here's hoping this information is incorrect.