Unless the recycle  bin has been turned off via Central Administration, can't
think of any.

that's kind of what I figured. We're looking more deeply
into the possibility of user  error.

Files deleted  in certain ways don't end up in the Recycle bin  either. For
example a file deleted as part of a workflow action will often not show  in the
Recycle bin.

Well, that is something I did not know.

I don't suppose there's a list of such methods somewhere, or a description
of the underlying reason...?

Any idea what might cause them
to not show? I've had workflows delete files  and they were in the bin. I wonder
if it's triggered by certain actions.

There's no definitive list, but the underlying reason is that files  deleted
through custom code don't always kickoff all the event handlers and system calls
that are called when a file is deleted  through the user  interface. Files in the
recycle bin  aren't actually deleted they are just flagged as deleted. Files
physically deleted through code won't be in the recycle  bin because they've
actually been deleted.

That makes sense. So if users are only using the browser UI, there
shouldn't be any of this "circumventing the Recycle Bin" business.