When you see your SERPS move radically up or down in the keyword tracker, is it usually before or after you see a corresponding movement in your traffic numbers? Is the keyword tracker usually a leading indicator or a trailing indicator for you?
I use it mostly for clients of course there its definately leading. I am not checking his or her stats daily. Also I use it for sites with commercial content. I dont really notice 100% difference between 40 visitors, or 50 daily visitors just because google ranked me high somewhere. Also I check the backlink checker quite often (again for clients) and therefore I think I see that page more often than that I see my visitor stats pages.
I think Will means SERPs (with the KT as the measuring tool) vs Traffic. And specifically whether you see rank increase before traffic increase or the other way around. I guess it's down to how often you check the KT. In general it will be leading I guess. For low-medium searched KWs it will take a few days before noticing accumulated traffic.
Here's a note in support of the trailing theory. During the current PR update, one of my sites shows up with a brand new PR6 on 14 of the Google datacenters and still shows the old PR5 in 3 Google datacenters, toolbarqueries.google.com, and the DigitalPoint Keyword Tracker. Of course I realize that this really has nothing to do with the keyword tracker and everything to do with Google's API interface. It's not that I'm addicted to watching my stats on the DigitalPoint Keyword Tracker, it's.... it's... it's... yeah... OK... got me.
I see it the other way. I see rankings in the keyword tracker that are 2-5 days ahead of what's on google. In some cases, #1 rankings that appear with the tracker --never-- materialize on google. #2 is as high as I can go (right behind manufacturers).