I accidently deleated the default home page in the main menu and it took me more then a hour hunting around to for how to fix  it.

So for search engine love.

To set the default landing in Joomla or to set home page in joomla.

1) login to administrator section ursite.com/administrator/

2) hoover of menu click on menu manger

3) Select main menu or what ever your main navigation is

4) select check box of the page of the navigation

5) click the star default button

wha lah that is the way you set the default page.

Update  

From My friend Mark Raborn

Geoffrey, you can also use secondary (non main menus) to place your "Default" home page and hide your main site navigation completely until a user ventures in. Completely hiding navigation is an option as long as the menu you chose to attach the Home Page to is active and the Article or Component set as "Default" is published. This technique is used sometimes to create a landing page free of typical NAV. :)