If you're interested in Windows Phone 7 development and were offline,
for whatever reason, today or have been sleeping under a rock, you may
have missed that the Beta version of the next version of the Windows
Phone 7 development tools (codename "Mango") were released today.
You can read more details at here then get it from this location.
Check out this video (sorry it's a bit wobbly-I hope you don't get sea sick watching it) to see what was said at the launch.