On May 21st at 10am Pacific time, Microsoft will unveil its next-generation Xbox console. And if this article were titled "What we know for sure about the next Xbox," we could end it here. Microsoft has been very tight-lipped about the successor to the Xbox 360, but that's about to change.Related StoriesSony vs. Microsoft game console wars reigniteYahoo revamps Flickr and offers a terabyte of free storage