Not sure what GP is thinking of, but type checking for Excel would be really nice:
ERR: A1 is USD/month, B1 is USD/user, so you cannot calculate A1+B1!
Not the unit definitions in a spreadsheet; I'd like a spreadsheet where each cell has not just a number, but a number with its unit. Formulas would be evaluated the way `units` does it. B1=3m; B2=4s; B3="=B1/B2" would give as value of B3 "0.75 m/s".
Ah, sure, that would be great. I'd say it would be useful in text based programming environments too though.
Agriculture would probably love a spreadsheet that understood units of measure and kept results as fractions.
Gotta love that a bushel of Yellow Corn is a different weight than a bushel of Oats.
All the grains are different. I had to hard code a table of those conversions for an application I worked on.