Any good PIM has a tasks element, but so far this has not been natively supported by Windows Phone 7.
Mango will however support tasks, and as usual will be well integrated with the other elements of the OS, in this case the calendar and agenda.
See the the feature briefly shows at around the 7:30 mark.
In the beginning of the video we also see a mysterious People icon in the camera interface, which may allow direct tagging of people from the app itself.
Thanks Robin for the tip.