So you want a fresh Ubu install and don't want to hunt-down all you currently packages....

..and reinstall them all one-by-one or write a silly script to handle them all. Well, here's a simple solution: 

Save currently installed packages:
 # dpkg --get-selections > packages.installed 

Save this off and then copy to new machine or back to re-installed, then do:

 # dpkg --set-selections < packages.installed
(* Note: You may want to prune the list of software that you don't want to install or is incompatible if newer version of OS, before doing import above.)

 Then do: # dselect

Also, don't forget to save and copy over your /etc/apt/sources.list of course.

 That's it! Simple, eh?