Microsoft has published a whitepaper titled "Enhancing the performance of Windows Internet Explorer 8". In the report the software giant claims that add-ons are responsible for over 70 percent of IE8 crashes, and that slowndowns in IE8 are very often caused by add-ons as well.
For our purposes, though, there's some interesting information about add-ons included:
Although browser add-ons can add great new features to your browser, they can also introduce performance issues if written poorly. Add-ons cause most browser crashes, accounting for over 70 percent of Internet Explorer 8's crashes. Slowdowns in Internet Explorer 8 are very often caused by add-ons—especially when you open a new browser window or tab.
It's good to see that only 30 percent of IE8's crashes are actually the browser's fault. Theoretically, IE8 users could simply run their browser in "No Add-ons mode" (iexplore.exe -extoff) and have a much more stable experience. In the real world, today's Web expects add-ons.