clarify when this module is useful and that it's not a cck field

This seems like an interesting module. From my initial review it seems like this module is useful:

0) You are building or modifing a form using Drupal's form API (you mention this point already on the project page so it's #0)
and
1) If you need uploads and want something like the core upload field
2) You aren't using cck or don't want to
3) The core upload field is being used for something else OR you aren't on a node form

Is that right? If so, I think the project page should have that information added. It is currently a little confusing when/where people might want to use it.

Also, the use of "field" in the title makes it seem like a cck field, but it isn't (is it?). I think you should clarify that http://drupal.org/project/filefield provides similar functionality for CCK and that this module is not for CCK but just for direct FAPI coding.