Multiple iCloud on Mac OS

Short answer is yes -- you can have a "joint" iCloud account set up on the Macs. On Lion you set up a Primary iCloud account (your "personal" one), and any number of secondaries. My wife and I do exactly this. We share Contacts and Calendars (which includes Reminders; on the Mac both Calendar & Reminder data are shown in iCal).

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You may also want to check this thread. This is somewhat technical stuff, but it's something you'll run into when you set up primary & secondary iCloud accounts on the Macs.

EDIT: I'm not sure if the iCloud preferences apply system-wide or if they are per account on the Mac. My gut suggests they are per-account. System-wide would be an invasion of privacy because of the nature of the content that is being synced. My wife and I each have our own machines.

 

My wife and I choose to have separate personal accounts for everything except iTunes purchases like Apps, Music, Music which we share the same account. Yes, you can have separate login ID's on each Mac and you will be able to setup separate iCloud Settings for each one.

Regarding the Calendar. On my account I created my personal calendar, a work calendar, a Golf Calendar and a Me and my wife "joint" calendar. I gave my wife read only access to my Golf Calendar but she has full read/write access to the joint calendar. We keep our Contacts Separate. Regarding Reminders, we do not really use it but I think you can do the same as Calendar. I do think a shared contact file (like calendar "sharing") would be helpful but that is not something that is provided with the normal setup. Regarding Calendar Sharing, you have to set that up with the Mac Calendar App and NOT on www.icloud.com.