If you go to the SimpleNote Page, you get an ominous: "we'll be back soon..."
It's only on their blog site that you find out: We should have mentioned: all is OK. All is great, actually. And all syncing services are still online. Our temporary absence from the App Store is merely the result of an unexpected complication with the forthcoming major update.
I went to the site because I read somewhere that Simperium is not to be trusted and might go away. Baloney ... though it might have been a good thing to include the information given in the blog entry on the Website itself.