chx is working on a very interesting patch http://drupal.org/node/332303 what by theory can totally redefine Drupal installer experience. The trick is to use a lightweight SQLite database what should be built-in to PHP 5.2 - so you will get your site running without providing mysql/postgres database credentials at all. If needed, you can migrate over to these "big boy" databases later. It simplifies Drupal code and removes the need for weird code trickery in the installer.
For UI it means we can dramatically simplify installer UI, cut several steps from there and basically hand over a almost-working site for the admin. Also, we need a proper messaging/notification system what later informs admin when the site needs a proper database to migrate to.
This discussion is a placeholder to provide UI design support and ideas for that zupa-cool idea.