I've now been using iPhone OS 3.0 for a week or so which is officially released today. Here is a quick recap of the new email and Exchange specific functions.
Spotlight Search You can now search emails from the iPhone, but more importantly you can also search emails remotely on the server. As an example my iPhone only syncs a weeks worth of email, if I want further back there is a 'Continue search on Server' which can search through all old previous emails in the Exchange information store.
Cut, Copy & Paste We hoped this would make version 2.0 but it's finally here. This works well for forwarding emails where you may want to snip an initial conversation. Find out more here
Landscape Keyboard This arguably should have been there from the start but it's there and does the job as expected.
Push of subfolders In settings -> Mail -> Your account, the final option allows you to be more granular and select specific subfolders to push (default to just the inbox like 2.0) This is useful for those with rules setup to filter into a subdirectories who had to previously remove these to be able to see new email.
There's still some obvious functionality missing (such as enabling out of office with Exchange 2007 remotely, something that's even been an option on Nokia's Mail for exchange for a while). Support for Exchange is now pretty complete, we've noticed a large increase in our own clients using iPhones and coupled with the enterprise features of enforced policies, remote wiping and deployment using the configuration utility the arguement of the iPhone being solely a 'media' phone no longer stands in my opinion.
Finally there is various other useful functionality such as MMS (yes MMS in 2009!) and data tethering which you can find more about here