I have my own dedicated server with Win 2008 STD, IIS 7. DNN 5.6.5 CE & MS SQL 2008 Express
The Compressiion by default is not enabled, there are two levels, server and site.
Server applicable to all IIS sites while site specific for that site.
Using IIS 7 compression features with Heavy caching and gzip compression on DNN with static content compression, improves the page load but on login one will get the following message (and can not login) on firefox (in IE blank page)
Content Encoding Error
The page you are trying to view cannot be shown because it uses an invalid or unsupported form of compression.
Please contact the website owners to inform them of this problem.
While with dymanic content compression enabled, it kills the CPU (there is a warming when enabled "may increase process utilization" my server has 1 GB RAM & celeron processor, hence in effect it killed my website.
If one would like to enable IIS Compression, suggest to disable gzip compression on the host setting and have at least 2 GB of RAM and a Duo Core Processor.