This issue is blocking's creation of a field formatter.
Splitting off from...
As I'm porting, there's a fair bit of D6 code in project_release to add custom "fields" to each file associated with a release. The prime example is the md5 hash, but there's also the download count and weight (relative to other files). From what I can tell, D7 doesn't make this particularly easy if we're just using a core file field on release nodes (which is what we want).
We can use a field_collection to represent each file associated with a release. This seems like a fairly straight-forward and natural fit. The files attached to a release are actually represented by a multi-valued field_collection. These field collection entities (that's how field_collection works) would have a single-valued file field, and separate fields (definable via the UI, in fact) for everything we care about md5 hash, download count, a sha1 hash if we wanted to add that, etc.