[frik]

It was very important for IE <=6. Early AJAX web apps like GMail ~2004 were quite hard to get right - avoid most memory JS leaks or the memory consumption got out of hand too fast. That was in the days of 512 MB memory and WinXP.

[tracker1]

I worked on an extjs app for a company where most of the users at the time where IE6 corporate wide (this was several months after IE8 was available. That said, there were such horrible memory leaks with references just in the nature of the application under IE (component<->JS ties wouldn't unwind/gc) it would quickly eat up memory after about half a day of work would need to restart the browser...

In the end a lot of people using the application would either have to restart during the day, use portable Firefox, which many actually did. Of course, there are/where many worse things in practice dealing with supporting IE<9 for relatively modern web applications. I'd still rather deal with that, than the v4 browser days.