1) In earlier versions of Access, you could use a command-line switch to
open a mdb file in Runtime mode. It sounds to me like accdr is just a
variation of that concept. You are right in thinking that this extension is
easy to change and provides no security in and of itself.

Making a accde file out of your accdb is what you want to do. Code is
compiled, all design elements are locked. This does not necessarily 'hide'
objects (you still need to set your startup options to hide db window, etc,
to do that), but even if they weren't unhidden code-bearing objects (forms,
reports) within a accde can't be opened in design view, even
programatically.  If you are marketing your effort then you'd be
distributing the Runtime engine with your app anyway.  The only security
threat in that case would be users who already have Access Retail. They are
the only ones that would even be capable of making design changes to an
accdb file. Runtime users can't.

2) The shift key bypass can be turned off.
http://support.microsoft.com/kb/826765  is only one source of information on
the subject.

3) AFAIK there is no alternative to Access 2007 runtime if you want to
distribute an Access 2007 app to users without Access 2007.

***************
2 notes of caution: when making a accde file, be sure to keep the original
accdb in a safe place. That's the file that you'll need to make any future
revisions before making a new accde since accde's are not editable.

When implementing a "turn off bypass key" strategy, consider leaving
yourself a "back door" so *you* can get back in. Alternatively, be sure you
know how to restore the bypass key setting from an external db.  My point
is: careful not to lock yourself out of your own app. That can be soooo
embarassing.

HTH,