Wikipedia

Figure 17-22. http://www.wikipedia.org
The Wikipedia page is relatively small and fast. It would be faster if the 10 images used as navigation icons at the bottom of the page were converted to a CSS sprite. Further, there are two stylesheets that should be combined. These simple improvements would reduce the page's HTTP requests from 16 to just 6: the HTML document, 1 stylesheet, 3 images, and 1 CSS sprite.
None of the images has an Expires header. This is the second-most
important performance improvement for Wikipedia. Some of the images
haven't been modified in over a year. Adding a far future Expires header would improve the response time
for millions of users, without adding much burden to the development
process when images change.
Also, the stylesheets should be gzipped. They currently total about 22K, and gzipping them would reduce the number of bytes downloaded to 16K.
Most of Wikipedia's images are in PNG format. The PNG format is frequently chosen over GIF because of its smaller file size, as well as greater color depth and transparency options. It's likely that using the PNG format saved Wikipedia several kilobytes of data to download (it's not possible to convert their PNG images to GIF for comparison because of the loss of color depth). However, even after choosing the PNG format, further optimization can bring the file sizes down even more. For example, optimizing ...