Interestingly, according to the graph at the end, IE6 was already well on its way out and they only accelerated its death by a few months. The real effect seems to have been stopping IE7 dead in its tracks, and almost single-handedly catapulting IE8 to the top. A most peculiar effect, despite the banner's promotion of IE8, since only IE6 users should have seen it!
I smell an untold story... maybe one of the other teams' banners was accidentally visible to IE7 users as well? Or did IE7 sometimes spoof IE6?
People who upgraded to IE7 were capable and willing to upgrade, and more likely to upgrade to a later version when available.
IE8 was the included browser with Windows 7, which was generally well received compared to Vista which included IE7.
The timing lines up within the release window of IE 8 (March 2009) and Windows 7 (July 2009), so potentially a lot of upgrade push from other things in the air at the time.
Edit to add: people on ie7 because it came with Vista probably had a more capable/pushy update system than those on XP with ie6; but I don't remember the details on how microsoft system updates worked at the time.
> people on ie7 because it came with Vista probably had a more capable/pushy update system
the people on vista had the pushiest update system of all: vista was terrible, and most users (especially organizational users) switched to windows 7 ASAP.
One big problem with IE7 was its asinine "This page contains scripts or ActiveX controls that could access your computer" warning banner that it plastered all over basically everything, including static .htm pages that didn't have even a single line of JavaScript, much less ActiveX. I got really tired of answering emails from users who were frightened half to death by that warning. It had the effect of desensitizing users to actual threats, or at least it would have if IE7 had ever gained much popularity.
It was a terrible piece of work and I was glad when it never achieved any significant market share.
I suspect a large part of the success of the campaign had to do with all the news sites covering the story. Those stories would have been seen by a lot of users, regardless of which browser version they were using.
IE7 did have tabs. In fact, it was one of the main features. They didn't make significant standards compatibility improvements until IE8, and only really in IE9. IE10 was the first one (since 6) to actually be comparable to other modern browsers.
IE8 was also the first IE to address a lot of the memory leaks that older versions had. DOM <-> JS access was referenced via COM interfaces and out of scope cleanup didn't cross bounds in earlier versions.
IE8 did have a really bad bug around the JSON.parse implementation though.
If you modified the Object.prototype or Array.prototype (which was common at the type with libraries like PrototypeJS) and used a rehydration function with JSON.parse, the runtime would throw an error you couldn't catch, and stop JS functioning. In IE 8.x ... almost worse, the JSON.parse function was locked... I wound up using a wrapper JSON.parse2 or something that was the JSON library edited to attach to parse2 for IE8, other browsers would alias parse as parse2.
I then used the parse2 in everything at that time. In the end, it sucked and I'm glad I don't have to do it anymore. IE8's quirks were what I would consider the last bad version of IE... since then it's been mostly okay on release, but ages rapidly, but enough turnover that you aren't on it too long. Until current IE11 as it's tied to windows releases, and some people/orgs didn't upgrade.
It's not measuring in six month intervals, that's just the scale at the bottom. There are peaks and troughs that are very clearly higher resolution than that.
More than that, the graph demonstrates how growth of IE overall dropped off. Up until then IE7 was replacing IE6. After that, no later version of IE ever topped the previous version.
I smell an untold story... maybe one of the other teams' banners was accidentally visible to IE7 users as well? Or did IE7 sometimes spoof IE6?