Thank you letters for multiple interviewers?

I had a 3 hour series of interviews at a University yesterday (July 3). In total I was interviewed by 10 people.

1. 20 minute introductory discussion with the department director (decision maker/prospective boss)

2. Hour long session with 5 members of the department staff

3. Half-hour session with 3 faculty/staff members from other areas of the college

4. Half-hour with an associate dean (decision maker's boss)

5. 20 minutes more with the department director

I'm a bit conflicted on who all to send thank-you e-mails to. Just the director? Him and the associate dean? The staff member who I believe organized/scheduled the interviews? Everyone?

I plan to send by e-mail (director asked me to send him my mileage as well so they can reimburse). The holiday has given me a little leeway, but I want to get them out no later than the 5th.

Professional opinions needed!!