At the moment I am developing a library, which is kinda based upon the jQuery one.
The main advantage being the function chaining.
so effectively you have your $() function which you can use to select your id
Then on the back of that you have your css() function to simply change a style or something
so in the end you can have say one element call and use it multiple times like so:
$('#test').css('display','block').css('color','#FFF');
as opposed to:
document.getElementById('test').style['display']='block';
document.getElementById('test').style['color']='#FFF';
So using that you have seriously optimised your code, but this is where it gets shady with people using jQuery as doing like 10 css changes like the above is slow when compared to just changing a elements class name, which is where i find people go too far with their jQuery.
And with building your own your taking into account all these small things, and not just saying fuck that I'm gonna do it easily by telling jQuery to do it all which is stupid.
I've also noticed the magazine I get Web Designer Mag, every article involving simple things they have jQuery which is pissing me off quite frankly and its everywhere.
Its so complex now you might as well learn Javascript
.