web service response caching: CacheDuration property doesn't work

if you want to cache the results from a web service call on the server, you’d think you just set the CacheDuration property the way you can with aspx pages (i.e. [WebMethod(CacheDuration=5)] and everything would be happy. turns out... no.

• web service output is NEVER cached for http-post web service requests, so you have to use http-get, which is disabled by default for web services and enabling it is not a recommended practice. great.
• browsers can stipulate “no-cache” in their request header, and the server will ignore its own cache for these requests. so even once you get http-get caching working, Firefox requests force the server to ignore its cache.
  

why this isn’t configurable on the server, i have no idea, but the short of it is: if you want real control over web service output caching, don’t use CacheDuration (i.e. write it yourself using Context.Cache, Application[] variables, or static variables). Context.Cache is a very cool class; you can specify an absolute expiration date, or dependencies on the cached content, so that the item is cleared from the cache when a dependency changes, or a sliding expiration date, like “5 seconds from last access”—