I've been using Planner mode for the last few months, to keep track of
appointments. I like it because it integrates well with Emacs, which
is my main environment. But I've decided it just doesn't cut the
mustard. It lacks two main things. Firstly, it can't do ICAL based
mail negotiation of meetings. Secondly, it lacks a nice overviewer. I
developed something which addresses the latter, but it's not
enough. So I keep on missing early meetings, because I didn't see them
coming up the day before.
In the end, I've decided to go for Google calendar. It generally
integrates nicely with mail, although I'll have to check my gmail
account periodically, which is a pain as I don't use it for anything
else. The AJAX interface of the calendar is quite nice; I don't need
to use it as rapidly as email, so that it's a bit clunky is not a huge
problem. Pity that right clicks don't work.
Moving current events is going to be a pain, though. I think I shall
keep planner, though, as a task manager. It's pretty good at that.