Apple definitely needs to get their act together re multi tasking, jailbreaking shouldn't be the only way to get this functionality.
It's funny but like i posted in my other thread, i think the Pre Card function is actually a copy of Safari Mobile's handling of tabs, or at the very least i think its where they got their inspiration.
i'm not sure what tupperwaretingler is referring to when she says Adobe, if she means Acrobat Reader or she means Flash, it would definitely be nice to see Flash handling outside of Youtube.
If you're just looking for something that can handle pdf books you should check out Stanza Reader.