Could someone explain to me why people even consider results collected via third-party browser toolbar to be relevant in any way? I mean... I don't remember ever seeing anyone in IT with a browser toolbar, and I remove them on the spot from my non-IT friends' browsers. Call it selection bias, but I think that most of the time someone has a toolbar of this type is when one's IT friends haven't have time to get to ones computer and remove it.
 - this is a serious question that bothers me; I can't see how this kind of selection gives any kind of representative sample.
I don't understand why something either has to be totally perfect information or totally useless.
Yes, Alexa information is pretty bad. Yes, it is easily faked. Yes, it isn't representative. Yes, browser toolbar usage is probably declining.
However, that doesn't mean that Alexa information cannot be used as an indication of big traffic trends considering there is a difference between absolute traffic levels and relative changes in traffic levels.
To give a different example. Let's say that you have a website with decent traffic levels and you collect browser usage statistics (e.g. 50% IE, 40% FF, 10% Chrome). Of course those are not representative for global browser usage. But if Chrome usage doubles for that group, it can be used as an indication for a trend in global browser usage.
Does it matter for this purpose if there results are fairly terrible? I'd be surprised if they were so bad that the reporting off the loss of half their traffic overnight didn't at least resemble some real loss of traffic.
well i wasn't talking about this case particularly.. i was talking in general alexa isn't considered nearly a credible source of getting info about sites. The obvious reason is that most people don't use toolbar. (browsers like chrome don't even have toolbars, browser toolbars are ancient)