Hi misty! What kind of dog is Maggie?
I've been doing research on interdigital furuncles as well. I have an American Bulldog mix that has some swollen spots between her toes as well. Interdigital cysts are supposedly very common in dogs with short hair, like bulldogs. Here's a good illustration:
She seems to have some other skin issues and my veterinarian initially suggested that the bumps may be due to seasonal allergies. She gave us a medicated shampoo for her skin and it has seemed to be helping her feet as well. I bathe her once a week. I'm not sure that the bumps are actually caused by allergies, but more frequent bathing definitely seems to be helping. A few websites I've seen have suggested epsom salt soaks for the feet but we haven't tried this yet.
Others have suggested surgery! Either to remove the furuncles or to fuse two toes together essentially removing the area where the furuncle would form. This seems like a VERY drastic measure to me! But you can read more about it here:
http://blogs.dogtime.com/dolittler-b...aken-therapies
For now, I am going to stick with the once a week medicated baths, good for her skin anyway.

May move to epsom salts if we have a flare-up.
Do let me know what your vet says when you see them. Good luck!