If you want to go with ASM 600 on. He popped up in an anniversary issue.
He was one of the main villains in a story involving a lot of other bad guys (ASM 642-647.) So he took a breather for 40+ issues.
He made a few intermittent appearances as a member of the Sinister Six (ASM 648, 659-660, 676) before the big clash in Ends of the Earth (682-687.) During those times, he always shared the stage with other villains. That part wasn't all that unusual, especially in the context of big bads (Look at how many issues Jackal popped up in from ASM 129-149, or Harry Osborn in Spectacular 176-200.)
Norman made a lot of appearances after the Clone Saga.
When he was the big bad of the Marvel U, his appearances were more restricted since it requires coordinating continuity with other titles. And his appearances wouldn't be as special given his role in other books (I think what Marvel did during Brand New Day with Norman worked pretty well in making his appearances in Spider-Man a bigger deal than would otherwise be the case.)
The major issue with Ock isn't how often he appears in terms of issue percentages, but how long the story's been going on (or how they shift from one story to another without permanent defeats.) But the reception seems positive.