Yes, on update user files are not effected (mostly). Applications (~/Applications or /Applications) files and user files (~/Library/Application Support) are kept in different locations. Most of the times only application files are updated and only developer decides what should happen with user files. If older user files are not compatible anymore and new version of application can't convert your user files to newer version, configuration files of that application will be damaged and removed. Application will start as first time and reconfiguring will be needed (if required at all). For instance Skype requires login information.
Other files not related with application is touched.
The Xandros system does not allow this extent of modification. You would need to install another Linux distribution on the Eee. Two distros that have a GUI similar to that of Mac OS X are gOS and Dreamlinux. gOS is designed for low-powered devices like the Eee, so it should be a good fit. Dreamlinux is not tailored for the Eee, but has low system requirement
Select, with a single click, a PDF file and and press the Command (cmd) and I keys to open the Info window. Half way down the Info window is a drop down menu labelled Open with... Choose whichever application you want to use and then click the Change All button. All PDFs will then open with your choice of application.
The first version of Mac OS X appeared in 2001 and was numbered version 10.0 it had the name "Cheetah". Subsequent releases increased the point number and had a big cat name.
10.6 "Snow Leopard"