We finally got to see Aero, the Longhorn User Interface. Overall, my interest is in how the flashy graphics will help people get their job done.  Having movies display in a document, and showing them moving in the thumbnails doesn't seem that useful.  Video in general is hard to get information from - it's difficult to condense in time.  I'm concerned the focus is on cool rather than productive. Good features:

• The back button is visible at the top of most windows.  This is a good feature to come from the rise of web browsers, since we know the back button is the most frequently used button.
• There are navigation breadcrumbs at the top of each screen (e.g. my documents, my photos).  You can click on any of these links and get a drop down of other choices at this level.
• In the search results it is possible to get a group of results, called a stack, which is indicated with a pile of papers that varies its height by the number of documents, as well as providing a count.
• When sharing a document the menu shows the name of others on the network that you can share with.  I liked this.

More troubling usability points:

• The side bar at the side of the desktop.  This looked a lot like the Active Desktop from IE 4.0 days (ignoring the opacity of the window).  It displayed an RSS feed, buddy list and a slide show.  I'm not really sure how far this progresses things.  The buddy list was not realistically large, the slide show was irrelevant (in terms of helping people be more productive).
• The top of each window displays the actions that can choose from, similar to XP (except they were hidden on the left hand side).  I'm wondering how useful this will be (I'm imagining you can turn it off).
• The bar at the top of each window displays the name and the back button.  It takes up about 10 - 20% of the screen real estate.  I'm wondering whether the information content justifies thie size.
• The menu has slipped from the top of the screen to under the bar area at the top of the window.  I'm hoping there will be some mouse 'gravity' around these menus as it would seem easier to go to the edge of the window for these key features.

Well, we've had clapping so far for the following:

• The CTRL+ALT+DEL login prompt.  I'm serious.  I think some delegates were so excited they just had to get it out of their system.