Our current datacenter is in New York City. Yep, where they make all that great salsa. So whenever you make a request to any Stack Exchange site, the internet tubes must connect from your location to our datacenter in NYC. We are not (yet) immune to the laws of physics, so depending on the distance between you and NYC this ... can take a while.
As John Carmack once so eloquently said:
The speed of light sucks.
A good CDN has a network of fast nodes all over the world.
With a CDN, when you make a request for, say, favicon.ico -- that particular file doesn't have to be delivered from our NYC datacenter. It can come from a server in the CDN closer to you. Yes, these files are usually cached, but you do have to retrieve them at least once and sometimes a few times a day. The resulting performance improvement can be quite dramatic, particularly for that first click!
We're currently evaluating our CDN options and we want to measure the real-world improvements of a few different CDNs.
Make a few requests to each of these links, using Ctrl-F5 / Command-Shift-R to force a redownload instead of using a cached version, and record the typical duration of a download.
In Chrome, you can see detailed download times via the "Network" tab of the Developer Tools, which can be invoked via Ctrl-Shift-I.
In Firefox with Firebug, download timing is on the "Network" tab, too:
The result in the Chrome screenshot is 576ms; in the Firefox screenshot it's 490ms.
Please use this Google form to enter your results.
With your data in hand, we hope to choose a killer CDN that makes Stack Exchange faster all over the world!
update: now with results! The percentages here mean percent better than sstatic.net which is our default CDN in NYC.