I've worked on some larger applications in javascript (though nothing incredibly large), and I can tell you if I had the choice of using any language that offered static and strong typing I'd take it in a heart beat. A small change in one place often means an error in some part of your code you didn't even think would be affected. I've loaded 65k LOC JS files in firebug and webkit's debugger chasing some error down that was happening in some piece of code that I've never seen before. All because that's how far my screw up managed to travel when there is no type checking or strong typing. In that particular case I had set a string value to something that was supposed to have been an array. Something like that would never have happen in, lets say C#, but "crap"[0] or "crap".indexOf("c") or ["c", "r"].indexOf("c") are all valid JS.
Dynamically typed languages offer a lot of benefits and a lot of burdens. Only you can judge whether you're willing to take those risks. Personally I am more comfortable with dynamically typed languages as they feel more natural and less programmatic, but this is just personal taste.
Nothing of this is related to the free-formness of JavaScript. Python and Ruby are also dynamically typed.
I have no experience with ruby, but python's advantage is in strong typing. Try and add an int and a string and you'll get a type error, JavaScript on the other hand will do it though. While maybe allowing you to write more expressive code, it does mean that errors become harder to locate, and when dealing with larger applications, I prefer being able to locate errors quickly.
