When you use gst-app (from cvs repository) or when you use gst-launch like this :
   gst-launch playbin uri=file:///c:/film.avi

you obtained this messages (on msdos and msys):
FAILED to play file:///g:/film.avi: Could not open file "/g:/film.avi" for reading.
E:\devel-release\src_releases\gstreamer\plugins\elements\gstfilesrc.c(981): (function) (): /playbin/source:
system error: Invalid argument

Effectively, /c:/path doesn't exist on windows.
To correct this bug, I propose following patch in gst/gsturi.c.
Function uses g_filename_from_uri from glib and the result will be fine on all platforms.
Perhaps, else case does not necessary.

Samuel

gchar *
gst_uri_get_location (const gchar * uri)
{
  gchar *colon;
  gchar *location, *unescaped;
  GError *err = NULL;

  g_return_val_if_fail (uri != NULL, NULL);
  g_return_val_if_fail (gst_uri_is_valid (uri), NULL);

  if (gst_uri_has_protocol(uri, "file") == TRUE)
  {
     unescaped = g_filename_from_uri(uri, NULL, &err);
     if (err != NULL)
     {
       GST_WARNING ("Failed to convert URI to a local filename: %s", err->message);
       g_error_free(err);
     }
  }
  else
  {
    colon = strstr (uri, "://");

    location = g_strdup (colon + 3);

    unescaped = unescape_string (location, "/");
    g_free (location);
  }

  return unescaped;
}