FWIW, I appear to have somehow appeased the nagware gods. I'm no longer getting these prompts. I'm not sure what I did to stop it, but I'm glad it's stopped.
Sorry, but verifying the email does NOT stop this insanely annoying notification. I get it on my iPad, and the desktop client (two different machines). It keeps prompting and prompting and prompting no matter how many times I verify the address. Please, someone make it stop before I give up and switch to a different note taking app.