Creative Writer 1.0 allows you to take field and research notes online and offline!
If you are offline, compose your note, click the "Save Local" button, and a local version of your note will be downloaded to your device. When you resume a connection with the web, just make a new note (click the "New Note" button), and then use the "Load Local Note" panel to access the file you stored locally. That file will then be used by the Note tool to populate the relevant fields; you can then click the "Save" button to save your note to your account.
If you have a Gold Membership, give the note-taking tool a try!