The team behind Hotmail have revolutionized their speedy e-mail system, trimming content on their pages to speed up download time and eliminated a network round trip on login for further speed gains. Their goal was to make Hotmail feel instant and they knew by speeding up downloads that it would get close to their goal. But that's not the only thing they had to do, even with today's fast internet, the network is the bottleneck and Hotmail needed to keep their customers from experiencing that latency.
Their approach was to get user data closer to the browser, and when the data is not available on the browser, get it there more efficiency and most of all, without the user noticing. The team also took advantage of the super powerful modern web browsers like Internet Explorer 9 and made them more app-like, by doing more work in the browser and less work on the server.
The Hotmail team identified three specific techniques to follow; caching, preloading and asynchronous operations.
If you'd like to know how they did this, check out the source for a very in-depth explanation, but if you like the TL;DR versions the improvements are actually pretty epic.
Comparing Hotmail from December 2010 to June 2011, the increases are;
Open message - 3.3 seconds down to 0.18 seconds
Delete message - 3.1 seconds down to 0.14 seconds
Compose new message 4.3 seconds down to 0.20 seconds
Pretty good, eh?