I'll be going as my geeky self. Only costume I have is a Jedi costume, and I think it would be too hot. And I've had issues with the lightsaber bits falling off. But I might wear my elf ears or fangs to annoy my b/f.
Uhm, this isn't the place to talk about it. But PM me about the costume and the saber. I've been with NY Jedi for a year and a half, and have done more than my fair share of con runs. So I should be able to help, if not point you in the right direction.
Comic Con '09 was held in February right after a snowstorm. You wouldn't know that from the amount of heat several thousand costumed geeks in the room. At least in October the Temperature shift will not be quite as murderous