The beginning of Thunderbird 3 planning

Calendar integration might be a feature requested by many users, there are users who use
Thunderbird just as a mail client. For those users, speed is the main factor. So, I worry
whether this integration (and other feature additions) could lead to a decrease in
performance. In that case, my suggestion would be to make Calendaring as modular as possible
and provide users an option to "Disable Calendaring support".