I'm able to vaguely keep in mind that you will find certain older versions of certain browsers which do strange things with GZip encoding - particularly I appear to recall a bug in IE which led to JavaScript sent over GZip getting mangled.

Vague memories aren't much practical use though. Does anybody know precisely what type of issues you will find and which user agents they affect?

Which browsers can handle Content-Encoding: gzip

Some common htaccess rules for any starter

# Netscape 4.x has some problems...
BrowserMatch ^Mozilla/4 gzip-only-text/html

# Netscape 4.06-4.08 have some more problems
BrowserMatch ^Mozilla/4\.0[678] no-gzip

# MSIE masquerades as Netscape, but it is fine
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html

Essentially you will find a couple of things you must do:

  1. Make sure the browser accepts GZip encoding. See Supercharging Javascript, Part 2: GZip Everything for any PHP example and
  2. Handle buggy versions of IE when confronted with secure content. See Supercharging Javascript, Part 6: The Internet Explorer Problem.

Although these good examples have been in PHP the concepts are universal. You do not say what language you are using.