Dear Don!

Thanks Helmut for the post.

You are welcome.

I guess that was a poor example I used wasn't it?

No, it was wonderful...

Do you think that URL's like (example):
www.example.com/all-about-mercedes-automobiles.htm
could ever be implemented in future plans for MLF? Do you think that would help with SEF?

I don't think it will be worth the effort. It would mean:

• a quite massive change in the code, and
  
• fiddling around with Apache's mod_rewrite module (being not that user-friendly) - which every Admin would have to do differently based on his/her file structure.

Have a look at these two threads from the phpBB-Communtity and an Able2Know-Board.

Even with short URLs the best you may get is something like
www.example.com/Cat-X-Thrd-Y-Pst-Z.htm
A blown up mlf plus any sophisticiated RewriteRule in .htaccess simply don't 'know' that this particular post deals with 'all-about-mercedes-automobiles' (the subject line will no be of any help either).

Since Google has no problem in indexing all posts - if you are avoiding double content - I would suggest to leave it just the simple way. People on the net are used to copy-paste long URLs.
Another problem would appear if you are submitting a sitemap to Google or Yahoo (what I did a couple of months ago). If more than about 5 Rewrite-Rules are to be followed in .htaccess, at least Google issues a Warning (whatever that means). So that's maybe another reason not to opt for short URLs.