If it is running Lion or the upcoming Mountain Lion,
the following can be synced on both devices via iCloud:
-iCloud mail (email@example.com) or items forwarded to
-Files using any Apple app that is available both for
iOS and OSX.
These are what Lion supports. Perhaps there may
be additional items when Mountain Lion releases.
Syncing of the Messages app coud be added since
Messages is going to be added in Mountain Lion.
See the iCloud support page: