Windows Mobile 6 (Crossbow) is out. I've already written about some of the benefits for developers, but now MSDN has a whitepaper with much more detail. BetaNews also has a good article about what's included in the new WM6 SDK, which was briefly online but has since disappeared.
Microsoft demoed the new OS on an HTC "Excalibur" S620, but don't run out and buy a T-Mobile Dash expecting an upgrade--due to licensing restrictions, it's unlikely many manufacturers or carriers will spend the time and money to offer upgrades to existing devices. On that note, LG became the first manufacturer to license the OS, for use on devices running on the Softbank network in Japan. Search previous coverage of WM6.