console.groupCollapsed("Application Log"); - what is it? If I "View source" in my browser I get a bunch of stuff in the end of my html output. It starts with console.groupCollapsed("Application Log");. 

I guess this is something Craft does automatically. Is it possible to turn it off when I launch my site?
This is something Craft only shows if your site is in devMode (http://buildwithcraft.com/help/dev-mode). 

If you use Firebug or Chrome Developer Tools for instance, it shows you a performance and error log.

By disabling devMode, it disappears. Do this by setting 'devMode' => false into your craft/config/general.php.