Here is the list of things that every productivity application should have:
Integration with iCal / Google Calendar - for those who rely on Google SMS texts as reminders
Powerful search – so I don’t have to waste time looking for the things that I need
Available on all platforms (Mac, PC, Android, iOS, Black Berry…) – so if I change the device, I don’t need to be left apart
Sharing options (Facebook, Twitter, @mail) – so I can share my thoughts with my friends without writing it twice and copy pasting
Tagging – so we can organize ourselves better
Reminders – so we can setup alarms without finding the native app
Offline access – so we don’t have to rely on internet in order for our system to work.