I do not use iCloud and do not want to have iCal send email when I accept into my calendar an event invitation or modify one.
Every time I accept an event, iCal tries to launch Mail, which I do NOT use for email (Thunderbird instead). I have already replied to who i want to reply to about whether I will participate in invitations and do NOT want iCal to respond.
I could tolerate iCal asking me whether it wants to respond or not, but can find no preferences or other modifications to control what iCal is doing.
This is very frustrating. Absent a fix, I believe I will have to abandon Apple software for calendaring and other applications.
Pro, Mac OS X (10.7.4), 2.3GHz Intel Quad Core i7