I use film when I need it's properties - the silver based chemistry for toning and preservation, the luster and appearance of a fiber print, the ease of influencing the print by what I do to make it and ultimately, the world of happy surprises provided by using a delayed process with physical materials. I think the bounds of physical reality provide as much structure to photography, as do the edges of the picture.
I use digital when I want it's advantages - the depth and clarity of the fine detail, the rich natural (or not) colors and the incredible boost to free form thinking that the immediacy of digital provides. Digital is capable of removing the boundaries of chemical photography, while adding others, giving rise to my oft repeated opinion that digital photography and film photography are two different media. Or at least dissimilar enough that they serve different needs.