Yes.
I sometimes write my own adventures (adventure outlines, really), sometimes wing it, essentially never use published adventures. However, I have taken interesting encounters from published adventures and used them outside their original context.
I use published settings for my Spelljammer campaigns because it would be waaaay too much work to come up with tons of worlds for the players to visit (and, intentionally or not, usually visit ruin upon). Spelljammer itself is a published setting, but I don't run it in AD&D 2e so it involves some homebrewing. Other than that, I mostly do homebrew settings or convert settings from other media, since I usually find those more compelling than tabletop RPG settings.
I use pre-made rulessets. I used to tinker a lot more with rules before I realized most everything I wanted had been done in SOME rules. I do mix and match at times, particularly among OGL games. I don't always run the rules for the setting/genre that came with the game, either.