As a recent Unity convert, one thing that (seems) to be missing from the chart is
1. Right-clicking the 'applications' tile opens a sub-menu with application categories. This is a nice and quick way to find apps by drilling down through the categories. In a way, it's rather like having the menus back. It's quicker than opening the finder and sorting using category drop-down.
2. Right-clicking the 'files' tile opens a sub-menu with your bookmarks (Music, Photos, Downloads, etc). Advantages as above.
Here's a good trick:
To start a new instance of an app from the dock, use the mouse's middle button, or click both buttons if using a laptop or a two-button mouse.