Unlike Tiger's iCal, Leopard's iCal has no info pane for events. When I was running Tiger, I had the info pane open all the time on the right side of iCal's window. This was very useful, and I consulted the info pane all the time, and it made it easy to check the info of a number of events quickly. The lack of an info pane in Leopard's iCal makes the app significantly less usable for more and requires a lot more mouse clicks or keystrokes. I've been using iCal for many years for all of my scheduling, so this regression has a major negative effect on my workflow. Until Leopard, I've never even given a thought to using a calendar app other than iCal, but now I am starting to consider it.