Saijo George made a preview of the 3 types of Push Notifications (Tile notifications, Toast notifications and Raw notifications). There is a lot of information about these notifications, but the cool thing about this preview is that there is extracted the most important information about them.
Push Notification is going to play a important role in WP7 and according
to the recently published UI Design and Interaction Guide for Windows
Phone 7 v2.0 there will be 3 types of Push Notification on windows phone
7
You can see the full story here.