Mac Settings and Data Syncing
The last MobileMe feature that won't be continuing in iCloud is the ability to sync settings and user data between multiple Macs. I've always thought of this feature as the unsung hero of all MobileMe benefits. In the MobileMe pane in System Preferences, the Sync tab allowed you to select from a wide selection of Mac account information and settings that you wanted to keep consistent across two or more computers (a desktop and a laptop, a work/school and home machine, etc.).
Options for Mac syncing through MobileMe included almost all of the System Preferences panes (which includes most of the Mac OS X preferences), items placed in the Dock and their order, Dashboard widgets, some application preferences, Safari bookmarks, notes, email accounts (with or without mail rules and signatures), and user Keychains (which store account information, passwords, and other secure information). Of course, personal data like contacts and calendar items could also be synced between all your Macs, iOS devices, and Windows PCs. All in all, you could make almost any Mac you used give you an identical experience and make setting up a new Mac extremely easy even if you weren't transferring any files.
I'd like to say that there is a simple solution to re-creating this feature, but the truth is there isn't. You can get a minimal approximation by using iCloud to sync some of this data (contacts, calendars, bookmarks, and such), but many of the more Mac-specific items simply aren't making the jump to iCloud. The best you can get out of the box is to use Apple's Migration Assistant to move settings (along with applications and user accounts) when you setup a new Mac, but that doesn't provide consistency over time.
That said, some Mac data syncing is possible. File Synchronization is a tool available through the Mac App Store (or the developer's website) that can sync specific files and folders. Those folders can be on a single Mac, on a cloud service that provide Finder access (Dropbox is perfect), or on two Macs on a home or office network or connected over the Internet using Back to My Mac (a MobileMe feature that is making it into iCloud).
In theory, you can use tools like File Synchronization to sync the preferences files for a variety of applications and some Mac OS X components. These .plist files are stored in the /Library/Preferences folder within your home folder, and most are easy to identify by the name of the company and/or product they are associated with. You can copy these files manually between two Macs to apply settings from one to the other, and you may even want to experiment with setting up an automated sync solution, provided you’re comfortable making under-the-hood changes to your Mac(s).
Given the sensitive nature of these files (and the fact that you may need to adjust the permissions on them to allow a sync tool to copy them back and forth), you should use caution if you decide to try configuring your own personal preferences sync solution, and make sure you have a good backup on each machine beforehand. You'll also want to test your setup pretty thoroughly and operate it manually until you're certain it can function without creating problems.
If you're really adventurous and comfortable using the command line, you may even want to check radmind, which is an IT-oriented sync tool commonly used in school and college computer labs.