Great idea, kat! I wish I'd seen this thread sooner. I've been weeding out too, and have recently mailed out to friends, and delivered to local shops, 5 boxes of books. There are still many more that deserve to be read, rather than sit on the shelf gathering dust, so I'll have to revisit that project again soon.
With regard to your suggestion of a book swap... What do you think about folks posting a title or subject that they're looking for, as well? That could serve as a good prompt for someone who would be happy to pass one on, but who may not be into sorting through the whole collection just now. Just a thought...