Hi Laurel – I sympathise, and certainly wanted us to offer that option. Unfortunately, we can’t yet.
We’re using the latest version of some open-source software, Drupal 7, to run the site. Irritatingly, the Notifications module used to offer daily or weekly digests for Drupal 6, but this hasn’t been implemented for Drupal 7! I was disappointed (to put it mildly…) when we realised this. Similar losses have occurred in other modules, and hopefully the Drupal community will develop them, then we can update the site. Unfortunately, the IOP does not have the expertise to do this work ourselves (or the funds to pay developers to do it for us).
We’ll let everyone know if we manage to update the site like this.