Ok, I did almost nothing for Drupal core to contribute. Sorry.
But I do a lot of hacking in our Drupal installation.

I made a path_class (I love OO). Which handles all paths for my drupal. The paths are relative and can be set by config now. It took a lot of hacking around, but it works perfectly ;)

My core drupal (with smarty) is somewhere on our server. A new account needs only some theming. Some config. Some symlinks. After copy and pasting an existing user.
It has just a few directories (splitted by root or html_public!) with only the user things. Anything else is in the central drupal-installation.

By making the paths relative and doing other things i forgot this moment, i got :
- paralel but central drupal installation (version-control)
- multiple site installation even in direct admin!
- splitting root and public_html files
- paths can be set by config-settings
- easy and small user-installations
- a new drupal-account has its own and normal direct-admin account!

Updating to the latest drupal-version is not always easy ;) But winmerge helps a lot.

Ohw and of course my debugging-tool which can also be triggered by the init-settings of a user. Constants like: debug_loading or debug_includes, debug_error, debug_backtrace and some if's at the right spot and voilááhhhh an error is easily found.

Some sites we made in Drupal:
www.gpdinterieur.nl
www.atica.nl
www.kheppum.nl
www.visionfirst.nl