I can't seem to get my iCloud Safari tabs to show up on my MBP (using ML). I have iOS6 on my iPhone5 and Ipad and it works across them, but won't show up on my mac. I've made sure the Safari option is checked, and I've rebooted my computer.
The iCloud button may be hidden. In the Safari menu bar, View > Customize Toolbar brings up the toolbar menu. Drag the iCloud button into the toolbar (make sure the Safari box is checked in System Prefs), and you should be ready to rock n roll.