Want your Ubuntu, Kubuntu & Xubuntu to have the same dock like OSX just install Wbar, Kiba-dock, AWN, Cairo-Dock, Kool Dock & SimDock. It will not be the same but it is similar.
To me, I’m using Ubuntu so I prefer AWN, but if you are using Kubuntu try Kiba-dock. If you like a light version, you should try Wbar.
1. Kiba-dock : Light and customizable and uses Akamaru physics engine making every icon on the dock has its own shape, mass, inertia & gravity. To download please go to the official website. You need 3D graphics, Compiz or Beryl in order to run Kiba-dock.
2. AWN (Avant Window Manager) : A dock bar for linux that needs 3D graphics, Compiz or Beryl. It has many efects. I could install on Ubuntu and Xubuntu but my friend Inzi had problem making it work on Kubuntu. So it’s your choice. Click here for more information.
3. Cairo-Dock : Well, it’s almost the same as all the others and It is compatible with Compiz-Fusion, Beryl, Compiz, and also Xcompmgr, but it can run without a composite manager (with fake transparency). Cairo-Dock can run under GNOME, KDE, and XFCE. (That means it can run on Ubuntu, Kubuntu, Xubuntu). Click here for more information. 
4. KoolDock : Similar like the rest. It’s based on KDE application and it requires 3D graphics, Compiz or Beryl. Since AWN doesn’t run on Kubuntu (please tell me if I’m wrong) why not give KoolDock a try? It’s always trial and error if you want to find out which is the best. Click here for more information.
5. SimDock : A fast dockbar for linux and works on most desktop environments. It does not require 3D acceleration, Compiz or Beryl. In other words, it is for slow computers or if you want your computer to work at the speed of light. Click here for more information. 
6. Wbar: Lightweight dockbar. If you’re using wallpaper changer, I do not recommend this software, instead use AWN. I would use this software but you have to tweak somethings before you can use it and be sure to download wbar-conf.
For more information on installing it, Google it. Usually the answers are there, or try to find in Ubuntu Forum.
Ubuntu/Kubuntu Help For Beginners.. 
Thanks
By: Guest on May 20, 2009
at 7:04 pm
Nice,very informative thank you! I’m trying simdock now. Maybe I will try Cairo later
By: Daniel on August 12, 2009
at 3:23 am
Very good comparison. You should use more tags so that your site pops up on search engines. Thanks.
By: Chetan Bhargava on October 20, 2009
at 7:30 pm
I have ubuntu as a base and downloaded kde (kubuntu) and xcfe (xubuntu) because sometimes i like different flavors.. but anyway, I have awn installed and have set it up to make it look similar to a mac, but awn does work in kubuntu, but if you have animations set, it does get choppy.. but for the most part, it works.
Anyway, this list and info is great! thanks for compiling it, stuff like this really helps others get the courage to drop windows…
By: andy on May 21, 2010
at 1:18 am