I’ve very recently had some experience with the legal system, which I won’t go into here, so when I read about Mark’s C&D letter and his question about what he should do I quickly formed an opinion. Change the name, Mark. While I am not a lawyer, I don’t see how this could not be a case of trademark infringement on your part. The same fellow has a trademark on both Magnetic Poetry™ and Electro-Magnetic Poetry™ with the latter being a computer program somewhat similar to yours.
If nothing else, contact the fellow and tell him you are willing to change the name of the program to something else but you are leaving the file names on the website as they are and see if he’ll accept that. Depending on his demeanor from there out then decide if you want to get contrary with him. It’s much better to avoid legal wranglings of any kind if they aren’t necessary.
Oh, and one more thing, I don’t believe it matters whether or not the notice they sent you was a form letter.