I love Portia Fitzsimmons, too... I was entertaining self just now, trying to imagine what creatures she could have turned out to be...
Evidently I'm having brain-farts, and can't think of any other examples, even though DS is full of them... those already given are good ones though. They built up Claude North as some intensely crucial and fascinating character (that's the implication I got from it) that it got irritating. They kept dropping his name into dialogue, as if we must care about who he is, as if we'd be bowled over when Mr. North finally deigned to grace us with his onscreen presense. Then he turned out to be a pushy, very young guy with a prematurely deep voice... That may be why they thought his character would take off, some sort of magnetism coming from being the youthful dreamboat type with a startlingly deep voice. All that's just a surface impression though, no indication of solid acting, and I guess audience response wasn't what they expected...
PT Gerard strikes me as a sort of DS practical joke on viewers! Drop him in, yank him out! What's fun is that no one onscreen has any clue as to why he's of significance to viewers...