You can even use made-up units ("hits", "people", etc... has a pluralizer). I made it as a personal productivity tool and have a slew of updates in the works =).
Ooh Instacalc! I really liked that app when I first heard of it (must be over a year ago?), thanks for reminding me of its existence, I'll check out how far it's come.
Hope the cross-browser issues got solved, I seem to remember that was my major hurdle (I'm on Opera).