The responses on this thread are really interesting. I come from a magazine and newsletter background, and have been at it for a long time. I remember when Pagemaker dominated the marketplace -- it actually revolutionized page layout. Quark came in in the late 80s, and by the early 90s, it had probably taken away dominance from Pagemaker. Throughout the 90s and into the early 2000s, it seemed as if Quark would never lose its cash cow of a business. I can't remember exactly when Adobe did the first version of InDesign. I wasn't paying attention. But I made the switchover with CS2, probably in 2005 -- just for a couple of projects here and there. We were stuck with Quark for other things for legacy reasons. The more we used InDesign, the more intuitive, and better, it seemed. You could get to the same place as you could with Quark, but it just took less time, and integrated really well with Photoshop. I don't do a ton of design work myself, but I can't imagine working in Quark. We don't even bother to update with new versions anymore.
There was a time in the early 2000s, when I was doing magazines, when I could have never imagined anything taking away the market from Quark. It's stunning just how unable they were to keep what they had. Too stodgy, too slow innovating and too slow keeping up with what Adobe did with InDesign.