how to handle being overqualified

I was wondering what everyones thoughts about being overqualified? I had a phone interview and I nailed it. He said the only concern was that he thought I may be over qualified. Money and benefits make the position worth it. I need to send a thank you letter tonight and was hoping to address it in that letter. Can anyone provide any recommendations?
Comments
Do you plan to stick with this organization for a while? If so, why? If not, then he's justified in worrying. He needs to know that you will be satisfied with the position you are hired for - at least for a reasonable amount of time. If you see a future for yourself at this company, express that and explain why.
Hiring is a pain for employers and management. My current position had 150 interviews before they hired me. 30 minutes x 149 = 75 hours of interviews. I interviewed with both a tech lead and a manager. So that 150 man hours. If you assume the guys interviewing you make $100k a year, or $50/hr thats $4,000 they spent just finding you. So time, money, energy, etc. Overqualified candidates make hiring managers nerveous for this reason.