Here is my 2 cents on the quark -vs- inDesign debate.
I have used quark since its inception, and resisted the "switch" for years. We have totally switched over, and will not look back any time soon. Quark 8 has HUGE problems/issues, and there do not seem to be fast fixes coming. We make many catalogs that have tables that have been cut and pasted into linked/flowing text boxes. That way the entire catalog flows thru the pages as items are either added or deleted. Now if I open any of these files in quark 8.01, the tables no longer work properly any more. The first table on each page is fine, but any tables underneath those on the page have NO text in them. Just blank fields. Completely IMPOSSIBLE to use quark 8.x with ANY files prepared in this fashion. And we have hundreds of these catalogs. Quark has been aware of this impossible situation for at least 5-6 months now, and yet no fix.
The other major issue with quark is transparency. It does not work like it needs to work. Photoshop files that have drop shadows on layers over transparent backgrounds do not multiply into underlying images in quark as expected. Quark ignores the layer properties in photoshop documents. You'll need to re-composite all pages in photoshop to get the proper effects. I have been told by quark that "maybe" in quark 9 it will be fixed. Not even in the quark 8 product life.
Regarding InDesign, I am "discovering" new things daily (being a new user). Each time I find/learn how to do a task I wonder why quark did not think of it first. InDesign is amazing. Very stable. Tables can ONLY be built within a text box, so the text flow thing is native, unlike the clumsy cut/paste in quark to do the same thing.
When InDesign creates pdfs, or when you output to print, it uses the photoshop engine to resample all your images on pdf/output. All your PDF files are small because the images are optimized to your settings as the pdfs are made. No longer have to open each image, resize to placed size, and re-import into quark at 100%. Done by the program at output. Now, I know quark uses its vista to render picture alterations, but it does not use the photoshop settings you want/need. In testing, I have sized images myself, and also did the image alterations using quark's vista, and there is a HUGE difference in the images at sizing. Quark's are very blurry, and soft. Indesign's look like you just resized them in photoshop. Crisp, clear. Again, not a fix coming within quark 8, MAYBE in the quark 9 product life I was told. Unacceptable.
I would recommend CS4 suite, and the new QtoID translator plug-ins. Much better bang for your buck if you are looking to upgrade/purchase. The new plug-in that works with CS4 translates quark 8 files, in addition to any older versions you have. Now, it does not work flawlessly. You'll may need to adjust things in ID after translation.
But, if you are like almost everyone I have talked to about switching, once you do you will be very happy. InDesign does almost everything quark does, and SO much more.