If you are not satisfied with the Unity launcher and want to use instead a dock similar to OS X, I suggest that you give Docky a try. Unlike the Unity launcher, Docky allows to display a dock launcher at the bottom of the screen containing all running windows with the possibility to add your favorite programs to this dock using the drag and drop feature.
Once installed and launched, docky will look like this on Ubuntu:
To install Docky on Ubuntu 11.10/11.04, open the terminal and run this command:
sudo apt-get install docky
You can then start it via the Unity Dash. If you prefer the dock to occupy the whole width of the bottom space, click the docky icon to bring up the settings window and select Panel Mode:
It will look like this:
You can also use the Docky settings window to start Docky automatically after login, select another theme, adjust icon size, change hiding behavior, add more docklets, etc.