HB, I am so glad you had a good time on your date. It sounds as if it went well I have never considered it bad manners in any situation to send a thank you note, but when it comes to dating, I think it is a little tricky. Clearly, you had a nice time and enjoy his company enough to consider getting together again as friends, but you aren't interested in him romantically. I would leave it up to him to make the next move...you don't want to give mixed signals. I think it is best to let the guy make the next move, whatever your intentions.