sixQuarks made a good point. Here are some things I asked myself when I first visited the page:
- Where do I write myself messages? Just on the website? Why should I use this website instead of just writing myself an Email, use Simplenote or the Notes App? What are the benefits?
I would make these points more clear and emphasize the main benefit in a bold and big headline. I also really like sixQuarks idea. Why not put a note-field on the first screen and show them how easy it is to use your service.
Another thought: Don't give so much space to the sign-in-field. Most people who ll visit your website won't have an account (yet), so my advice would be: Place a big sign-up-field there instead – or an input field where people can send themselves messages already – and move the sign-in to the navigation bar.
As somebody who loves good design: You should work on the design. Use Typekit (Open Sans, PT Sans are very popular these days and make a big difference compared to all the Helvetica websites) and use a larger font-size in general.