If you run a Joomla site where you want the new content items by default to be published on the frontpage, you're out of luck, this is something Joomla don't let you set in some config file. In the normal Joomla work-flow the Publisher (or someone ranked higher) will decide/need to decide if and when put a given content item in the frontpage. You may need this (or you're bored already needing to go back again and again in editing mode just to click on that select box...).
Here's what you can do about:
If you use Joomla 1.0.* t his can be achieved with a single change in the file components/com_content/content.php. Search for the line:
$row->frontpage = 0;
(it's somewhere around line 1849) and replace it with:
$row->frontpage = 1;
This will enable frontpage auto-publishing of all your contents. Note: although this may be useful for publishing news in the frontpage, it may not be what you want for when you create articles that are not to display in the frontpage (In this case, you need to uncheck the frontpage publishing box). You should consider which one is the most common case and decide on the best option for it.
With Joomla 1.5/1.7it's a different story. Hold on, will be back with a tip addressing that too!
Update on December22, 2011: Back with the promised tip: Go there, download it, install it, and enjoy!