With version 3.0 of WordPress, the much anticipated feature of Child Themes was integrated or some might say it was improved, since it was actually possible to use it. I like to show you an example based on the new default Theme TwentyTen how you use it. Another example can be found in my WP Basis-Theme (SVN); currently not HTML 5 version.
The function of the Child Themes can be applied basically in every theme and the new features facilitate access and creation of a Child Themes. Before there were also possibilities to change a Theme without changing the actual files of the theme. With the support of Child Themes this is now completely independent and we can use a theme that can be updated without a problem, and you can still realize your own ideas.