As I'm reinstalling my MBA, it's a first time I launch osx installtion myself. It is good to list the things I have to do/install here.
1. Update via software update.
2. Install Xcode.
3. Install brew http://mxcl.github.com/homebrew/
4. Install rvm https://rvm.io//rvm/install/
5. Install rails + pry
6. Install Adobes
7. Install samsung driver http://www.seagate.com/support/external-hard-drives/desktop-hard-drives/...
8. Enable git color
$ git config --global --add color.ui true
9. Install Sublime text 2 and do some setups http://www.sublimetext.com/docs/2/osx_command_line.html
10. Install mysql, use the mysql package that was downloaded. After installation, install startup item + prefPane. Finally, add path in .bash_profile PATH=/usr/local/bin:/usr/local/mysql/bin:$PATH.
ps. This is for osx 10.6