If you are running a web site resource usage and performance can play a big part in your site visitors experience, namely their experience in how long it takes your web site’s pages to load. There are modules called GZip and mod_deflate for Apache web servers that will compress the data requested by a web browser using Zip compression to create a compress stream that is decompressed at the browsers end. This is server wide and effects all web services on the server. The result is less data sent from the server to the browser. This has two huge affects one, it can reduce bandwidth usage by as much as 75% and two, decrease page load times by a factor of 4. Here is some data on this BLOG:

URL: http://mbrando.com

File Size Comparison (in bytes):
Original size: 61964 bytes
Compressed size: 19077 bytes
Savings: 42887 bytes
Percentage saved by
Transfer speed
3.2 X

Dial-up Modem 56.0 Kbps – 8.645s vs. 2.661s
DSL/Cable Modem 256.0 Kbps – 1.891s vs. 0.582s

( Above data by: port80software.com )

Here are some links with additional information

GZip works with Apache 1.3x and Apache 2.x.
GZip Site Home
Compressing Web Output Using mod_gzip for Apache 1.3.x and 2.0.x

Apache 2.x comes with a module called mod_deflate.
Apahce 2.x documentation
Compressing Web Content with mod_gzip and mod_deflate