I have Quark on my system to convert old Quark documents to Indesign so that I can work on them - haven't used Quark from scratch for a while now, so guess I sold my soul to Adobe. There are still quite a few companies that use Quark out there though.
We spent a few bucks to get the Markzware Q2Id plug in, worth every penny as i haven't opened Qxp for nearly 18 months (just opened it now to see when the last file was opened and boy did the opperating space look cold and forbidding)
I use both, swings and roundabouts and all that. At my old firm my boss used to do everything in Illustrator, though that was mainly him lacking the skills to use either QX or ID. Mind you, this is the man who starts colour profiling at the printer, checks output colours under pink fluorescent lighting in an area where the walls are painted bright yellow, has never calibrated his display on his mac, and insisted that all artwork be supplied in pantone colours. Bob pope, what an arse!:icon_biggrin:
The guy above, is to me, as Mr Miyage is to Daniel San, and taught me both. And I have to say I prefer InDesign purely for its Adobe friendly interface. Although the Quark logo looks better in the dock than the purple square when bouncing next to eachother, pretty sure I've seen it jump slightly higher too, but that might've been the effects of a caffeine overdose, he taught me about those too. Dangerous man.
I believe Quark is still the editorial design tool of choice. Indesign has taken the corporate and institutional publishing market, because its work flow is better and, frankly, because it's easier to use. It lacks Quark's flexibility, though, and publishers still expect Quark.
At least that's what my wife tells me and she is, of course, always right, except when I'm wrong.