I have recently switched from using Outlook (which I have used from way back when it was called Exchange) to using the combination of Thunderbird and Sunbird. It's doesn't fall short. It's faster to open than Outlook and uses a lot less resources. It also has a lot more intersting features and it's calendar application uses an open standard format (the Apple iCal format). What that means is that any calendar application could be written to use that format and your Sunbird appointments could be displayed and updated through any third party calendar using the same file format. You can also have different calendars, have them hosted on a web site and therefore share calendars with people and/or have access to your calendar from any computer. It also support extensions the same way Mozilla/Firefox does, and therefore it can have additional features added by anybody who can write the extensions.
I don't miss Outlook one bit. Sunbird/Thunderbird do what I need and better.
