I'm running a campaign set in Ptolus. I have, however, used none of the pre-existing adventures that were included. None seemed to interest my PCs. However, I HAVE inserted a big chunk of one module from Curse of the Crimson Throne, and another large chunk from WLD (region B, spliced and diced). And I ran Sunless Citadel, somewhat modified. The players kind of ditched that one most of the way through, as they found what THEY needed, and never bothered the druid. An acquaintance sent me a massive chunk of sewer and dungeon maps and notes, which have been "somewhat" explored.
I'm designing my own "Buried City of Ptolus" right now, for future plot and adventure, although there's a chance I'll never use it, sadly. I intend to continue pushing the sewers, which I'll run more or less sandbox style, as a potential adventure place. I'd love to have them end up in the were-rat lair I downloaded...
So I said I use about 70% modules. Other campaigns have been more like 30% module; especially as the PCs go up levels and build their own storyline, it becomes much harder to "reconstruct" a module to fit without doing major work on it - at which time I'd rather just use the map and do my own adventure design. Modules become bits that get tucked in as side-dishes so I have time to write my own main course.