By default, the MobileMe service only pushes out changes every 15 minutes. That means you may have to wait up to that long for your changes to be pushed. Way to long. Here's how you can edit that value to anything you like so that the changes get pushed more frequently from MobileMe.

Open a Finder window and navigate to the directory: /Library/Preferences/ByHost. Note that this is the /Library directory in the root of your hard drive, not the one in your personal home directory. Once there find the file called com.apple.DotMacSync.your_MAC_address.plist. (If in doubt on how to get to the correct directory, you can just use Spotlight to find the com.apple.DotMacSync.your_MAC_address.plist file for you.)

Once you find the file, right click on it and choose to open it using the Property List Editor application. You'll then want to click on the triangle things to find the property called AutoSyncInterval. This is the number of minutes that elapse between pushes. Set this to any integer value (so 1 minute is the shortest interval) you want and save your changes. This will reset the frequency of the pushes that take place with the MobileMe push service.