I was talking to one of my candidates this morning about a thank you note she was going to write. I was relieved to learn that she was hand writing a short note instead of emailing it. Email is great, but not for thank you notes. I've found most emailed thank you notes candidates write to their interviewer to be too long, too much about themselves (instead of the company), and are often hastily and poorly written.
I prefer a short, legible hand written note on good stationary. Keep it simple and to the point. Mail it immediately after an interview - it has a much bigger impact than any email.