Not that an Apple cloud service is any sort of secret, but paying $4.5 million for a domain confirms something is coming. It sounds like it might be a separate service from MobileMe, which would be surprising.
Link to the trademark registration: <a href="http://tess2.uspto.gov/bin/showfield?f=doc&state=4009:7n9955.2.1" rel="nofollow">http://tess2.uspto.gov/bin/showfield?f=doc&state=4009:7n...</a>