Digging through the the Mac OS X Lion beta, Consomac found strings for "Castle", which looks to be the codename or the next generation MobileMe.
Complete your Castle upgrade
Click OK to open System Preferences and complete your upgrade from MobilMe to Castle
"Castle" could be the placeholder for iCloud, if Apple chooses to go with that name, but given the "upgrade" language in the string, it looks to be more than just a name change at least. We've already conjectured about what could be included in the next generation MobileMe, and that WWDC 2011 in June could be when the announcement is made.
What remains to be seen is how Apple will tie sync with cloud storage, and what if anything will bridge it's still disparate social services including Ping and Game Center?