In case you haven’t figured it out yet, Drupal is best if you learn ALL the ins and outs of the product. and that means learning how to:
- Create subthemes from existing themes
- Customize modules as needed and sharing with the community
- Customize CSS (Very important)
- Theme functions
- Become a member of Drupal.org for the ridiculously low price of 30 bucks.
- Get involved with the community
- Probably a lot more
Here is a great site that will help you get started with some of the more serious development work that can be done in Drupal. With Drupal, it seems to me that knowing where the HTML that you see in Firebug is generated is an enormous part of making the platform work for you. So check this site out.
I also recommend trying out Aptana Code Editor.
Firebug for Firefox
Chrome’s Element Inspector