Question: Is there any opensource samples of JQuery usages of StackOverFlow-like sites...... 

Any help in this direction??

Answer: 
You can make the same effects by using [plugins](http://plugins.jquery.com/).

* <http://www.jqueryplugins.com/>
* <http://www.sastgroup.com/jquery/240-plugins-jquery>
The web is full of them. For starters, I recommend reading through the [Documentation](http://docs.jquery.com/Main_Page).