Can I sync calendars and contacts from two mac accounts with one iCloud account? The reason I want to do this is that I have two Mac accounts for different purposes, one for fun and one for work. However, there are some types of data (e.g., contacts) that I want to share. Moreover, I have a single iPhone used for both work and personal, and I want both sets of data on the phone.

The two Mac OS X accounts are on the same machine. I have no connected either to iCloud as yet until I get a recommendation on what will serve me best.

What do you recommend I do?
You could have two iCloud accounts and sync both calendars to your iPhone.
You can achieve the same result if one or both of your accounts is on Yahoo, Gmail or Exchange, without the need to create two iCloud accounts.
If having two calendars that you can switch on and off is your concern, you can have one iCloud account, under one user account in your computer, and two calendars, named "Fun" and "Work", and reduce the hassle.