One of the big problems with using the Drupal Aggregator for ArborBlogs was that it doesn’t support Atom out of the box. My initial fix was to create an Atom -> RSS converter using Magpie but this weekend I was able to set up Drupal to use Magpie for RSS and Atom parsing without the need for a mediator.
I don’t know how the Drupal community deals with contributions, I’ll investigate that when I have a chance, but if you’ve got a Drupal site and want to try out my modifications, you can try out my modified aggregator module. It creates modules/aggregator/aggregator.module so you’ll need to move modules/aggregator.module out of modules for it to work.