Data cost is known to be one of the main reasons for not using mobile internet. Or that is; the uncertainty of the data cost. So, why not help the user by doing as much as possible to cut the data transfer??
I have made a simple test site to illustrate the importance of this issue:
This is just a quick mock up using php. The test is only zipping the markup and not the style sheet and images on the page. However, it shows huge savings in data transfer!
The next interesting question is if the gain in speed of download is lost in extra processing time on the device…..