If there is one application I miss most since switching to MacOSX it would be Outlook.

I made a decision to go "Web 2.0" when I bought my mac mini and Google Mail has been my primary interface for over 2 years.

This is one application on the Windoze platform done correctly and for all practical purposes has become quite the standard in enterprises across the world!

Now that I am moving my communications to Facebook it'll be interesting to see how this pans out...

• easily programmable (I've personally played with the COM interface myself and it was pretty easy to learn)
• lots of productivity add-ons
  • I miss my (paid) GTD Add-on for sure
    • snooze emails
  • I am curious what the Mission Control add-in is like.
• easily syncable (i think it's in everyone's best interest to sync to this platform at minimum!)
• PIM data in one hierarchy - email, contacts, notes, tasks
• UI that actually is done well
• offline use
• features to play with: colored flags, importance, categories, filters, folders, and other meta-data...

this is just cream of the crop - i am sure I'll think of others...

calling any facebook application programmers out there! Like to experiment with a GTD app! ;-)