I have a solution I use, though it's a bit hackish. I wish Apple had just left the "local mail" feature in...
Here's what I do:
1. Make an Account
Make a new POP account. Set the server to "localhost", and enter anything for the username. Set the SMTP server to "localhost", of course:
*Important: Under the "Advanced" tab,
turn off "Include when automatically checking for new mail". Otherwise Mail.app will squawk about failing to connect to the POP server at localhost, which would be fair, since you're not running one...
2. Point the Inbox to the local mbox
* In the Finder, open up ~/Library/Mail/POP-arkham@localhost/ (or whatever)
* Open the "INBOX.mbox" package.
* Delete the "mbox" and "table_of_contents" files, if they exist.
This next part is key:
* Go to the Terminal, and navigate to the same folder (by doing
cd and dropping the folder onto Terminal).
* Type
ln -s /var/mail/arkham mbox
to point the mbox to your local mail.
If you stopped here, it would work at first, but Mail.app wouldn't notice new mail. That's because Mail.app relies on the "table_of_contents" file to keep tabs on changes - if you get new mail, but the table_of_contents doesn't change, Mail.app won't notice.
So do this: Type
touch table_of_contents to make a blank file, then
chmod u-rw table_of_contents to keep yourself (or Mail.app) from changing this file any more.
When Mail.app sees the blank table_of_contents, it will refresh its view of the mbox.
That's it!
The one problem is that Mail.app always thinks the mail is new. But it's handy, anyway.
For going the other way (reading your Mail.app mail from pine), see
this machosxhints.com article and my scripts towards the bottom.