Interview Follow-up
Always follow an interview with a brief professional thank you note. You may want to reassert your interest, offer another example of your skills, or refer to topics covered in the interview.
It may be appropriate to write an e-mail thank you note IF most or all of your communication with the employer has been done electronically. However, you are also demonstrating your ability to behave professionally with this potential employer's customer, clients, students, etc. so you may want to model good professional behaviors with a little formality by writing a snail mail thank you instead.
Here are some examples of thank you letters/notes: