This is simplicity itself, and that is the beauty of it. Full kudos to the people at “Lies, Damned Lies” who are now, or will shortly, be on my blogroll and I encourage you to check out the original post
The mysteries of measuring marketing response, part 2: Landing pages.

Suppose you have different “campaigns” going - promotional campaigns, for the sake of simplicity .. but it could be just about anything. The sort of thing I cover in my “Stratified Marketing” post - oops, looks like it is not up yet, keep an eye out; it will be shortly.

Well, the first thing you need to do is collect some data. Data that will allow you to estimate efficacy, differential response etc.

You can use referrer logs, but the suggested technique is to create a page that is only referenced by your marketing campaing (no internal or external incoming links) and “decorate” the url with meaningful parameters - these are ignored by the server.

For example, http://dsanalytics.com/index.html?hello%20fred is perfectly valid .. it just goes to my home page (but of course you would not do that in the context). The parameters can be picked up in an analysis of the logs.

Seems sensible to me