Some views on using email on the new iPhones:
MS on iPhone: Exchange IMAP is Pull, Not Push
This item below reflects the "we won't allow it" view of the IT bureaucracy. We'll see how long that lasts as more executives buy iPhones...
Apple iPhone E-Mail Issues Concern CIOs
I'll bet many organizations that do not currently support IMAP will be short term... The email vendors are starting to advertise secure IMAP support for the iPhone (at least on the PRWeb) - get yet another email address!