Functional details can really matter and add up to either a horribly frustrating experience or one that is fluid, productive, sensible. For example, keyboard shortcuts for a date picker or in-field auto completion (similar to Google Suggest). Coding for CTRL + A, Arrow UP/DOWN, HOME/END buttons, etc. all add up big time for those power users who are data entry experts, 8 hrs a day, 40 hrs a week. They increase productivity and keep the data entry pro humming along swimmingly well, minimizing errors, and maximizing output.
Yes, it’s tedious, but working out the interaction details like tab, shift, control, spacebar, etc. can have huge dividends for your user cranking away at her job someplace…