File Picker is missing a Sort by... feature. See this discussion: http://moodle.org/mod/forum/discuss.php?d=194664

This is how the File Picker sorts and displays files (as far as I can see):

Upload a file: you are using the Windows (or Mac etc) file viewer were you can at will sort by Size, Type, Date, etc.
Private files: files are sorted by Name (no other option available)
external Repository: files are sorted by Date (no other option available)

What seems to be missing from the Moodle 2 File Picker is a "Sort by..." feature for Private files and external repositories.