Also without understand DOM and crap related to that it's just too easy to use each and then $(elem).appendTo('#div') in every iteration.
EXACTLY. jQuery can, in many ways, be a replacement for thinking and understanding the DOM. And it is no speed demon, so care must really be taken.
Yeah, just to clarify that DOM is no speed demon but jQuery is speed demon. With 1.4.2 release it's the fastest javascript framework around beating even Dojo 1.4.1.
I highly recommend checking Paul Irish's slideset about jQuery performance guidelines at
http://www.slideshare.net/paul.irish/perfcompressionIn my opinion javascript is the most misunderstood language and after I have been reading and coding with it, it has become my favorite language along Ruby. It's just so different because it doesn't work like languages I have been programming before. Like for example anonymous functions and being able to do weird shit like like var run = (new Function("return "+code))();
With Opera 10.6 and IE9 all browsers support web workers, javascript will soon perform things you wouldn't believe.