I have 4.11 and 3.32, and still use 3.32 for 85% of what I do.
Quark 4.11 offers several new features,including a new Bezier (freeform pen) tool, a way to convert text into picture boxes, and more flexibility with text (for example, the ability to flow text along a bezier path).
It also has a completely redesigned Print dialog, which I am not at all fond of.
When you install Quark 4, make sure you update to 4.11 and install the Quark 411 Fixit XTension, which fixes a bug where Quark will mark all the linked graphics files as "open" to the operating system, preventing you from modifying or deleting them.