1. Make it visible when the text cannot be saved. Nobody wants to lose his work because of Wi-Fi glitch. In my version of notepad I implemented this with a light yellow frame around the textarea. I'm sure there's a better way to do it.
2. Imagine you could type a note into an address bar, hit Enter and have it added to your notepad. It's easy to implement, and it works really great for saving page URLs. Here's how I did it with a similar service of mine. Define a keyword search (e.g. "g hello world" - Google Search, "s hello world" - add a note), in Opera it's trivial - right-click the text area, select Create Search, and pick a keyword, I guess in other browsers it's doable too. The POST request carries the name of the page and a note to be added. It might sound simple, obvious, useless, but try it and there's a chance you'll love it.
3. List of my pages in the sidebar. Like, when I prefix my pages with "alisey." they go to the sidebar. E.g alisey.links, alisey.snippets.