It's angels on the head of a pin, this whole challenge of tracking UUs etc. And it's not just for blogs -- I can't tell you the hoops we used to go through to try to figure out which numbers were right -- and then trying to reconcile, say, ComScore to internal (and decide *which* internal to use etc. for that matter). And then you'd have analysts, say, looking at ComScore transactional ($ sales) numbers etc. Yikers. Best call is to say "this is what I am using" and stick with that -- which for us, publicly, was ComScore because they are public (sorta) and have credibility. Then, just stay on top of any methodology changes your chosen service provider makes so you can accurately track traffic growth or decline, which unless you are selling page views is what matters anyway. - Stuart