It appears Apple is the only company around that doesn't use Microsoft Exchange. Apple's recently released iOS (not to be confused with Cisco's IOS) 4 apparently wasn't tested with Exchange at all. Many users are reporting slow e-mail sync, and apparently Exchange server admins are none too happy with the load these devices are putting on the Exchange server – much more than the old OS did.
Of course, you cannot downgrade a device that has been upgraded to iOS 4. iPhone Operating Systems are signed by Apple at run-time and Apple refuses to digitally sign anything below iOS 4 now, so if you upgrade your device, you are stuck, unless you are willing to jailbreak your device, and right now, you can't jailbreak an iOS 4 device that was not jailbroken prior to the upgrade.
That leaves you with Apple's solution: a configuration profile that modifies the settings on your device.
Unfortunately, the configuration profile is unsigned. Configuration profiles make critical changes to how your device operates. Therefore, Apple supports signing them so their source can be authenticated. Too bad Apple doesn't bother with this itself. Rather, Apple's recommendation appears to be that users download and install random unsigned configuration profiles found on the Internet.