Google Analytics Usage on top websites:
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I must say that they do a great work on keeping that code. The asynchronous syntax while confusing at first is a very clever way to push code execution and loading way down on the queue, so browsers don't delay the page loading to register a GA pageview. It's clear that the GA team takes great care when it comes to how fast and seamless their code is.
The one point that still bothers me a lot regarding performance are the Google Analytics cookies. Let's take a look at what GA cookies look like:
"__utma=96182344.347392035.1326382423.1326382423.1326382423.1; __utmb=96182322.214.171.1246382423; __utmc=96182344; __utmz=96182344.1326382423.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none)"
This is a minimum GA cookie. It can get longer if you use Custom Variables and Google Website Optimizer. But let's settle down with the minimum for now.
According to Google SPDY whitepaper the average HTTP request is 700-800 bytes long. That means that GA Cookies represent about 25% of that HTTP request size. The moment you notice GA is present in about 50% of top websites you notice that useless GA cookies going around the internet represent 12% of all HTTP requests.
I've posted a bug regarding this issue on GA-Issues a while ago. The idea is to use HTML5 localStorage to store the cookies on browsers that support it. Still it has attracted no attention so far. This bug fix could easily make the average HTTP request around 5% faster. We're talking about the average speed of the whole internet.
The real picture is not that bad, since this only affect HTTP requests and not HTTP responses and that's where the real data is. Still it's funny to see something that huge going around unnoticed.