ShawnAd, here it comes:
1. when user1 and user2 were on exchange 2003, they could correctly see each other's calendar (not talking about free busy, I'm talking about CALENDARS, from Outlook). If I move them "together" from 2003 to Online, they are still able to see each other's calendar, because hybrid mailbox move brings permissions. If i move only one user, then calendars are not accessible anymore.... until of course I don't move the other mailbox as well
2. as mentioned in 1. yes, they are. They have been shared with Outlook. as usual
3. Outlook 2007 SP3 with Novembre 2012 updates as per Office 365 requirements. I don't have Outlook 2010 to make some other tries.