LAS VEGAS--You wanted push notifications in Windows Phone 7 Series, and you're getting 'em. Above you see a little blue bar at the top of the phone's screen that popped down, alerting you to something happening in another app. Click the bar, and you're taken to it from whatever app you're in.
We'll have to see what ends up in the shipped version of the Windows Phone OS -- we wouldn't be surprised to see the look of the notifications change a bit -- but the principle is sound. That's also in line with how we think multitasking will work -- not so much a number of apps running in parallel, but in sequence, hopping from one to another.