The last 2 days my emails have not been pushed. I only receive email when I open the mail application. I'm receiving my emails immediately on my blackberry 8900 from the same Yahoo account and this was the case until 2 days ago with my iphone 3gs.
I deleted and re-added the yahoo account but still no push. I also reset the iphone with no change. Other push notifications are working fine, i.e. IM+ for AIM and Yahoo IM.
i agree with charlie, i've got a free yahoo acct that pushes only when it feels like it. with a blackberry, it works a little bit different in that the email is pushed to you by the bis servers. with the iphone, yahoo pushes straight to you. at least this is how i understand it to work. i just signed up for the 60 day free mobile me trial, and it seems to be working really well. push is very quick. not quite as fast as my berry i dont think, but pretty quick. of course, now, i cant forward my yahoo email to the me acct because it wants me to upgrade to plus for that. *sigh* oh well, gmail is working this way and that makes me happy.