The diary has obvious uses in keeping track of on-calls, meetings & other events. I tend to have a fairly fixed timetable & relatively few events each day - hence I prefer to view a week at a time. A variety of views are available depending on what suits an individual best. Actually the diary shown is not the one supplied with the device, but is a third party application that I prefer.
The address list can be sorted into 15 categories - eg. personal, business, & one for each different hospital I am involved with. One contact number is chosen as the default to show in the initial list, but additional numbers, a full address & notes can all be stored with each entry & accessed by a single tap of the screen. Having gradually built up a list of the numbers I use most often, I can now save a lot of time that previously would have been spent looking for phonebooks & numbers or else ringing switchboards.
The "To Do" list works exactly as it sounds & again entries can be sorted into 15 categories - eg. work, homework, supermarket etc. and listed in order of priority or date due. Notes can be attached to each entry. Items can either disappear or remain crossed-out once completed.