Three things that have sealed the deal for me on whether I'm going to use the referrer field.
- These two posts — here and here, they key phrase being "The key lesson here is that you shouldn't be messing with the viral aspect of your product".
- Doc Searl's referrer logs. Note the presence of Technorati's home page, NetNewsWire and Radio Userland. Sorry, I don't have one thousandth the budget of Dave Sifry or John Robb: they define the playing field and if they're going to use it, so are the other players.
Since I've added Jäger to the referrer field, hits and downloads have had a substantial increase. If Jäger's showing up in your referrers a lot, it's because a lot of people are hitting your site with it. Note that the vast number of these hits are probably adding very little load to your server, since Jäger is very well behaved with regards to If-Modified-Since and ETags.
The referrer page will link to '/user', a page that will explain what Jäger is.

