I was raised on QuarkXPress since version 3. I've loved it and I've hated it.
Since Indesign came out, I've not been in the page layout biz, so I've only had tinkering-level experience with it. Tho, at my current job, the media lab SWEARS by it over Quark. Of course, if i learned it, I'd have to learn my keyboard shortcuts all over again (so...so many shortcuts). But InDesign's interface is clean and functional.
Indesign is quickly replacing Quark as the industry standard. Now, Quark has Quark 7.0 in beta right now, and it's got some nice improvements. But I still think they stopped progressing in the late 90's. InDesign knowledge is going to be very useful in the future.
The design-for-print industry is always changing and new demands are made monthly. Adobe has done a good job responding to those, while Quark hasn't, to put it simply (perhaps bitterly).