If you have an iPhone and it is running very slow after updating to iOS 4 and you are using Active Sync (Microsoft Exchange or Google Sync) then click on this link from Mobile Safari (on your iPhone) and install the fix Apple released. Be sure to restart your iPhone after you apply the update. I'm so mad it took this long for me to find this but I'll save you the sob story. If you want the details hit up the source below.
My phone was almost unusable until I applied this. I couldn't even make a phone call. At one point I deleted my Gmail account and had to go without contacts. Boy was that fun. Remember when you used to have to memorize phone numbers? Anyways, mail and contacts started syncing immediately after I applied the fix but my calendar is not syncing but if I get a fix I'll post it up. Anyone else having problems with iOS 4 and Active Sync? Post a comment.