Google-drive – Web-based Dropbox and Google Docs integration

I think this is fine if you are only testing something for a few friends. However, there is an issue with using too much bandwidth if you try to host something through your public folder that becomes too popular. As per https://www.dropbox.com/help/45:

There are currently no hard limits on public bandwidth usage. We do, however, have an automated system for detecting and flagging unusual amounts of bandwidth usage. We will send an email notification whenever an account is flagged. Once flagged, public links will be temporarily disabled and users who use the links will see an error page instead of your file.

Simplenote recently added Dropbox syncing as a premium feature:

Dropbox is a great way to sync files. When you link your Dropbox account to your Simplenote account, all your notes in Simplenote will appear as text files in the Dropbox directory of your choice. Thereafter, your notes and files stay synchronized as you make changes. Syncing happens in both directions.

In my experience so far, the feature has not worked completely. The changes I make to the text files in my Dropbox folder do not get pushed to Simplenote's cloud. But I am hopeful that this will be fixed soon.

Notational Velocity, a 3rd-party text editor that syncs with Simplenote, also supports storing its notes as text files, which you can put onto Dropbox. But this solution is far from optimal since this ties the Dropbox syncing entirely to the single computer that you use NV on.

I realize this answer only addresses one part of the your question--the Simplenote side--and entirely ignores the Evernote side:)