The technology world is filled with binary problems and you can expect that every jump forward may set you a little back. iPhone users who updated to iOS4 recently may have found this out when certain Exchange based Email, Contacts, and Calendars did not sync in the way that they had normally done to their iPhone. This actually affected all of Apple's small scale mobile line from iPod Touch's to the iPhone 3Gs and even the new iPhone 4.
In response to this Apple has released a "configuration profile" that will essentially increase the amount of time that they take to sync to these sources, thereby hopefully remedying the problem. To do this you must first go to the Apple website with Safari on your iPhone and then open up the attachment for the configuration profile from Apple. From there you go through a simple install process to get the iPhone configuration profile onto your newly updated iPhone, which may or may not solve the problem.
We will have to wait to see if this actually remedies this sync problem in all cases, but it does indicate that there may be a need to migrate to different email service.