A Senior Manager over at Redmond's Microsoft campus got hold of a Nokia Lumia 900 running avery early build of Windows Phone 7.8 and decided to tape the new homescreen and upload it to YouTube.
He demonstrates the live tiles resizing in all three modes - small, medium and large. Doing so also changes the amount of information that the tile gives you. For example a small SMS live tile gives you only the number of unread messages, while a large one also gives you a quick preview.
Microsoft has also posted a dedicated page, detailing the new features that will come to existing 7.5 users via the WP 7.8 update - you can find it here (note that an account is needed to view it).
Among the highlights are the new Start screen, the currently around 100 thousand apps for WP and information about the Lumia-exclusive camera enhancements and a new way of sharing contacts and track data usage.
Source | Via