Changes in UI in SharePoint 2010

General Improvements:

1. Reduce use of tables in HTML
2. Cross browser support-IE, Firefox, Safari.
3. UI upgradtion is separate frm database upgrade.
4. Client object model- Javascript and silverlight.
5. CSS is splited in multiple files and downloaded what are necessary only.
6. Javascript can load when u need.

Master pages and Lay out:

1. Application pages use dynamic master pages

The Ribbon:

1. Always on the top of the page and fixed in that position even if u scroll the page.
2. U can navigate in tabs.
3. U can remove any OOB controls
4. U can add new controls anywhere in the ribbon
5. Most of the controls available out of box like Button, Checkbox, Label, Textbox etc, But the control that is absent is Ribbon Gallery control.
6. You can customize server side and client side as well.
7. Also you can entirely replace the ribbon.

Dialog framework:

1. All dialogs are modal
2. Contents load in iframe
3. You can drag with in the browser also.
4. It can also be maximized to the size of the browser.

Theme:

1. U can add a power point theme in SharePoint.