If you’re expecting a long hack about how to get it working sorry you won’t find it here. Ubuntu just works in VirtualBox except for one not so obvious error message on first boot.
I couldn’t get a screenshot for some reason but the error message you will get on first boot of any ubuntu distro (desktop or server) in VirtualBox is:
Starting up ...
This kernel requires the following features not present on the CPU:
0:6
Unable o boot - please use a kernel appropriate for your CPU.
Huh? Yeah me too. I’ve encountered this issue before I just forgot the fix so I had to google it (again). The fix is:
- Power-off or shutdown the running virtual machine instance
- Select the “Settings” menu option from the context-menu on your VM instance (mine is called hardy lts in the screenshot)
- Then from the General tab pane select “Advanced” tab pane
- Enable PAE/NX
That’s it! You now have a useable ubuntu virtual machine running in OS X. yay. This is listed as a “Known Issue” on the ubuntu wiki
Disclaimer: Steps may vary on your guest OS. eg. it might require 50+ clicks and a cold boot when using winblows 
Actually I use VirtualBox to do programming in Ubuntu and many other distros. Its actually just as simple as you say in Windows (I use Windows Vista). I noticed you didn’t talk about installing the Addons which if your planning to run Ubuntu for long periods of time comes in handy as it get a bit faster plus you can use seamless mode.
Hey Alpha_Cluster. The post was merely meant to describe the fix for ubuntu installs on first boot BUT hey you just mentioned addons in your comment so I don’t have to any longer. Cheers