Hello Rafael,
I think that this is a very good idea. I suppose that you are thinking of functionality that mail.yahoo.com is using. It only works on IE and not on my Linux Netscape. You can type your email to somebody and in the header of the textarea you have couple symbols that format your text whatever way you want it. (Like bold, list etc.)
For the future it would also be valueable to integrate simple mathematical functions (i.e. the main algebraic etc.) over MahtML for example.
You might want to check out the following
thread too.
