I personally thinks it's better to post in an old thread rather than start a new one. I mean, by posting in an old thread, you've got the rest of the previous discussion right there, whereas in a new thread people have to chop and change. Also, by starting a new thread, you are just adding another thread, crowding the forums. Probably not too much of an issue here, but I'm on some other very large boards, and it can lead to having a dozen threads all about the one thing.
I'm an expert at sexual innuendo. I could keep it up all night.