I asked this question over in general, but I think it might have been a bit convoluted. When I think about it, quite simply what I want is a Related Pages module.

Example:'
1. Create a page
2. There is a tab called "Related Pages"
3. This tab has a table of every other page in the system
4. This table has checkboxes for selecting pages that related to the current page.

Anyone aware of anything out there?

AFAIK no module for it, but it would be pretty simple to add. A quick overview

On your Page class define both the many_many relation and belongs_many_many

private static $many_many = array(
'RelatedPages' => 'Page
);

private static $belongs_many_many = array(
'Related' => 'Page'
);

Then in your getCMSFields add a GridField instance for managing the RelatedPages relation. An example that covers relation grid fields is http://programs.edchipman.ca/silverstripe-modules/sortablegridfield/many-many-example/

Hello Will

You are really awesome.

Thanks Will,

I'll give that a shot once I've finished upgrading this particular site to 3.x.