Time is running out for OmniFocus customers who are still using MobileMe to sync their data. Apple is going to shut down the MobileMe service on June 30, 2012 and users need to switch their syncing services before this date.
To help you transition away from MobileMe, OmniGroup lists several alternative syncing solutions, including its own sync server. Once you have chosen an alternative to MobileMe, OmniGroup also has a set of instructions that show you how to change the sync settings within OmniFocus. If you run into any difficulties, you can email or call their support team using the contact information provided on OmniGroup's website.