@wilk I totally agree with you, it's all a personal choice.
But as you can see in my previous comment, this protip is not about performance, it's about learning native methods, so you have an idea what happens in the background. When you ask front-end developers if they know JavaScript, 80-90% say they do, while they only know how the libraries are supposed to be used and not how everything is processed in the background.
I know these are what you might call "micro-optimizations", but that's not the point of my protip ;-). The point is that you don't always have to rely on jQuery to handle basic DOM manipulation/selection, Thanks for the comment though, I appreciate it.
Probably best to prefix it with sudo ;-)
@moak What doesn't break in IE6? :p
btw useful statistics on IE6 => http://www.ie6countdown.com/
More information on your subject: http://www.paulirish.com/2010/the-protocol-relative-url/
Tip 2 can be replaced with http://be2.php.net/array_unique