Chris actually has some interesting elements there that you should consider - terms etc. are important to a lot of independent contractors.

Yup, absolutely his idea inspired me. It was the single creative element that made me realise that I can make invoicing a bit better than the other folks.

Besides a history and autocompletion... I can't think of anything else to improve this app.

Are you planning on adding PDF export? Or, at least, something like "email this invoice"? I don't interact with my clients in person, so just the ability to print an invoice is clearly not enough to make me use your app.

Yup.