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Isn't Lion required for Photo Stream in iPhoto or for iCloud support for keeping Bookmarks, Contacts and Calendar synced with your iDevice and your Mac?
 
Two different questions there

To sync iCloud between your mac and iPhone or two macs (bookmarks, contacts, photoStream, docs), your macs would currently need OSX 10.7.2 update. there's no word on an iCloud patch for OSX 10.6

For iTunes wifi sync you just need iTunes 10.5 and iOS5 on your iDevice, since that is not a part of iCloud.
For iCloud sync between iDevices, or for iCloud backup of the iDevice, they all just need iOS5
 
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