JQuery in Action : what's the advantages JQuery over Extjs

I use extjs for some while, but I never use jquery before. to me, the extjs UI is pretty fancy and decent, this is the most important part I am using it. I strongly doubt that UI parts of jquery can catch up with JQuery? any comments? and I want to know some advantages jquery over extjs. for ex, learning curve.

thanks a lot for some brief answer.

I simply look at the license for ExtJS and immediately look elsewhere.

http://www.sencha.com/products/license.php

jQuery's license is much more reasonable.

http://jquery.org/license

I think the jQuery learning curve is quicker, but the jQuery UI core is smaller than that of ExtJS. Once you get into jQuery UI plugins all bets on usability, functionality, support, versioning, extensibility, etc. are off, since they're contributed and of wildly varying quality. There are great ones out there, and if they do what you need, that's great.