From my upgrade experience, nothing has been lost in the process.All application settings are the same, all the applications are there and all the files are still here.Sometimes these can indicate hardware problems, but otherwise may suggest software configuration errors that may migrate with the system during the upgrade.Granted the refresh of OS software may in fact clear some of these problems up, but it may be more assuring to install the new OS over a known working system configuration.I was mighty pissed when I found out that the OS X Lion upgrade wiped out my entire development tool-chain.However, with help from a friend, I discovered that the tool-chain had instead been moved into the Downloads With "Components" selected, you will see a list of downloadable components. You will be prompted for your Apple Developer userid and password.But did you know that mac computers has a weak partition to begin with so if you notice that a lot of the data is missing go to clock and date and if they are wron than you need to use the tuneup diskett to reinstall all of your drivers then readjust the time and date then redownload what you had before the error this is the way to fix this problem.Good luck i hope i was helpful to you The OS X update should not erase any data.
At the very basics, reboot the system into Safe Mode and then use Disk Utility to check the hard drive for errors.Whoo I had this issue too, where even after I install XCode4, there was no gcc in my path. I reran the XCode installer and now /usr/bin/gcc is a symlink to /usr/llvm-gcc-4.2/bin/llvm-gcc-4.2 as it should be. See gist.github.com/1096750 for me trying to do that to link to gcc/make for use with OSX brew.Download and install from the App Store as per my other comment.First, the only true requirement for upgrading is to ensure your system meets the minimum system requirements for running Mavericks.If your Mac can run OS X Mountain Lion then it should run Mavericks, and in its announcement today, Apple reiterated this includes the mid-2007 i Mac, Mac Book Airs from late-2008, and the Mac Mini from early 2009.