John Resig is the creater of jQuery. jQuery is java-script library. What makes it really wonderful is that it lets you do a lot of dom modification is just a few lines. Additionally most of the cross browsers issues are taken care of by the library. That means you spend more time doing what you want.
No. This site does not use jQuery. But I use it at work, and find it awesome. If I am to redesign nunespascal.com jQuery will surely come handy.