Is ESRI's ArcGIS platform of programs available on Ubuntu? I love open source and if I could I would love to try and migrate to this open source OS.
At present ArcGIS Desktop is not supported on the Linux platform but you can install Server platform software on Linux such as ArcGIS Server.
For more details please check ESRI FAQ: Will ArcGIS run on Linux?
See also Desktop GIS for Linux (in Linux Journal)
Right now, only the backend software is available for Ubuntu (ArcServer, ArcSDK). This is because many enterprise-level companies run Ubuntu, SUSE, or other Linux servers and Windows workstations. However, ArcGIS is not the only fish in the sea. Using free and open-source software, you can do almost everything that ArcGIS can, and a number of things that it can't. If you already know how to use ArcMap, the learning curve going to Quantum GIS or others is a lot less steep than you might expect.
I personally use an open source software stack on Ubuntu for a lot of my work. Once I have time to learn the Python syntax for Quantum GIS, I may leave ArcMap behind.