This from their FAQ:

Sharing

Can other people see my scores on Noteflight?

Only if you want them to. A new score on Noteflight is always private, and only the author can see it. To change these settings, visit the Sharing panel.

Can other people print my scores?

If you let other people read your scores, then they can also print them.

Intellectual Property and Copyright

Does Noteflight automatically acquire some kind of rights to music I create within it?

No, we don't. Placing your music on Noteflight does not change your ownership of your intellectual property.

When I share music with others, am I giving away my copyright?

No. Your work is still yours, but by sharing it you are granting others certain rights to view and download, and (if you so choose) to edit and adapt the work. See our terms of use for the legal details.

Can I use Noteflight to share other people's copyrighted music?

If we are notified that you are using Noteflight to infringe someone else's legal copyright, we will notify you and remove your content from the system as required by law. If you persist in doing so, we will permanently block your account from Noteflight as detailed in our terms of use.

My music is being shared on Noteflight without my authorization. How do I ask for it to be removed?

Please file a valid DMCA request, as detailed on our copyright policy page.

No, they don't claim ownership of what you post up there.

Working with cover tunes is not a problem as long as you keep it private so I guess that means you can use it to create all the non original scores you want and print them out for yourself. Sharing copywritten songs is no different that putting a cover tune on Youtube. As long as nobody complains no problem but if the rights owner complains then it comes down.

Looks like a cool app to me and is one of the growing number of reasons I just may have to get an IPad.

Bob