I don't have an iPhone, but I do have a question...

What if you've sorted the list (by sender, for example) so the 'natural' place for the new message is half way down your list? Will it determine a travel delta or something similar to determine whether to snap you to the message?

I'm guessing you can't sort your email.

I've run into this problem before (how to orient a view of a list that is updated in the background). Google, for example, partitions the list into 'all items' and 'new items' so if you've paged half way through the list, the incoming item is added to the 'new items' view and a visual indicator is made that a new item exists (cf. Google Reader).