...ur point?, my Jb iPhone has multitask via backgrounder and battery doesn't change that much, on the other hand a stock iphone still runs Mail, ipod and safari at least without user knowledge and that doesn't change how much battery the phones drain...so again, ur point?
it's not the battery you should be worried about. it's the memory. besides, it's not like you will leave everything you're multitasking on for 24/7. you're just asking to crash your iphone.