I personally love the iPhone and believe any business user could get what they need out of this device.
I am currently a student and use my phone for: texing (A LOT), web browsing, iPod (24/7), email, games, and occasional apps like Digg or Facebook.
Here is what I found on ArsTechnica's iPhone 3G shortly after it's release:
"If you're a business user, then we feel the answer is no, it's not worth it. The original iPhone was not made to be an enterprise device, and the new iPhone isn't either. Although some baby steps have been made, BlackBerry users will find themselves frustrated with the lack of complete Exchange support and may even end up returning their devices, or at least carrying an iPhone alongside a BlackBerry. We already know several who have done this, and it will happen to many more." --
ArsTechnica