I definitely have a segregation of apps/content. I no longer have any video content on my iPhone, and I don't have any music/podcasts on my iPad (mini). About the only games I use on my iPhone are a solitaire game and a backgammon game for which I haven't bothered to spring for the HD version because each time the game hands me my a$$ I'm pretty sure it's cheating, and if you think for one second I'm gonna give some cheating ba$tar....
Where was I? Oh, yeah, games. I use the iPad for a handful of "big screen" games (racing, flying, shooting...).
I also have a number of writing/notetaking/drawing apps on the iPad that practically wouldn't make sense on the iPhone.
Regards,
Tom