A couple of essentials I just read in the Posterous.com FAQ.
To tag your posts place tags in the subject field in the following format:
((tag: apple, gadgets))
To ensure your corporate (or any other) email signature gets ignored place the following at the end of your post (BUT WITHOUT THE SPACE BETWEEN THE “#” AND “end”. I had to put that there or it would have been cut off.. that’s the whole point right!)