To email or not to email?

As you can tell by the title of this post I am pondering the appropritaness of email X to tell him that I was disappionted about tonight. I guess I would make a bad passive-aggressive person, as I feel this need to tell him how I feel. For some reason I could not on the phone tonight (cell phones are no good for communication sometimes- all those deadspots on a highway can really kill the nuances of a conversation). And this would not be to bitch him out about tonight, but rather to convey my disappointment and at the same time not seem distant and unfeeling (as I have sometimes been accused of in the past).

When it comes to gender relations, where is that fine line between coming off as too needy or too aloof?