I use only the summary card but have noticed that several unused fields get added to the Custom Fields sections of my posts. I'm also unable to delete them (I've tried deleting each blank field but upon "update" the blank fields return.
The additional blank fields are:
I understand that this provides flexibility on a per post basis, but in a future release I would love the ability to specify that only TwitterCardType and CardImage were available at the post level. I use Custom Fields for many things on my site and the additional blank fields make it harder for me to administer my site.
Please let me know if you have any questions or if my description is not clear. And thanks for a great plug-in!