A simple example would be:
Resulting in one HTML page with an embedded image:
Viewing the page with Firefox with the YSlow plugin
Comparing the original and the base64 files against each other
The original image is around 25.5 KB large while the base64 version is around 34 KB. The data size was increased with around 33.3%.
Encoding other various files I got the following results:
Based on these figures a typical base64 encoding increases the data size with around one third (36%) of the file size. However, this size can of course later be decreased by using GZIP compression.
According to several sources, the Data URI scheme are only supported in modern browsers, really starting from Internet Explorer 8 and forward (Internet Explorer 7 does support it, but with some heavy constraints).
As an experiment uploaded my test page and used Browsershot to give me a screen shot of the page from 65 different browsers on various operating systems.
65 different combinations of browsers and operating systems
As displayed above, it works on Firefox 3.6+, Chrome 9.0+, Safari 3.2.3+, Opera 9.54+ and Internet Explorer 8+. But not in Internet Explorer 6 or 7. However, there is an alternative solution available for those browsers as well.
I won't cover this question in this blog entry. However if you are interested here are some links that highlights the advantages and the disadvantages: