I have an iPhone, a MacBook Air and a 27" iMac. On the iPhone and Air, iCal and iCloud seem to be functioning correctly. I can invite attendees, the invitation goes into the attendee's calendar, and the info is shared across both devices.
However, on the 27" iMac (Lion), after working ok it all of a sudden told me I couldn't invite attendees because there was not an address card for me in the address book. So I created one--and now it will only send invitations via mail (ie, they do not go directly into the other party's iCal). Any entries I make on the 27" iMac do not show up on my other devices. iCloud has never worked perfectly from that computer, although it appears to be set up correctly. Thoughts?