Question: I'm toying with the idea of a pet project..

I wanna make our coffee machine remote controlled by a web interface.

The idea is to hit a "make me coffee button" and have it poll the router get the MAC address list to see who's in the office and send them a growl notification (we all use macs) asking if they'd like coffee and then doing something with a relay to turn the coffee machine on..

Can you recommend a programmable wifi relay or small embedded system for this?

Answer: 
Not as far as the client is concerned, no.

The difference for the server is that you have the full power of PHP to do something with before initiating the download, which is not the case if Apache handles the download directly. It also means that the whole cruft of PHP needs to be loaded and executed before a download can start and it'll occupy one PHP process until the download is finished.
***If*** your "normal" download would supply *those exact headers*, then ***no***.

However, a number of things could cause the server to decide to send different headers:

* If **[gzip](http://en.wikipedia.org/wiki/Gzip#Other_uses)** is turned on (and browser accepts it)
* If the [request](http://en.wikipedia.org/wiki/List_of_HTTP_header_fields#Requests) sent an **If-Modified-Since** header and the content has not been modified
* If the server decides to send a **Last-Modified** time
* If the server has some other sort of [cache-control logic](http://httpd.apache.org/docs/2.2/caching.html)