For date fields:
1) Ability to enter T for Today, Y for yesterday, NW for next week and the date will automatically be calculated.
I previously discussed in another thread a problem with "next month" or "one month ago". What date is "next month" for January 30 or 31 or "one month ago" for March 30? Although a programmer could arbitrarily pick a standard definition, there's no guarantee that users would apply the same definition.
2) Ability to set a field so it automatically picks only a weekday. The programmer has to be able to specify "move forward" or "move back". For example, for filing deadlines (court, tax, government reports, etc.) you probably would want to move back to Friday, but for sales call follow-ups you would probably prefer to move ahead to Monday.
Related to that, it could check against a table of pre-defined "special" dates such as Christmas and dates the programmer adds.
For instance, years ago we went down to the state court in Houston to file something and were surprised that the courts were closed. It was a
state holiday that is a legal holiday only in Texas. (Yes, the programmer could write a "CheckHoliday(Date)" function, but this is such a common need it would be nice to just select the option when creating the field.)