Dmitry Buterin makes a very good point that adults, like children, learn by watching others. He extends the analogy to web-applications and mentions about Zoho Sheet too.
Using online office applications is still very much a novelty. Thus, many users might not be asking themselves "Do you have feature X?" or "Which online app has more features?" but rather "How the heck can I make practical use of this in my life?"
The websites for Numbler and Zoho Sheet websites provided no obvious clues about what I could do with their products.
Now, that's absolutely right. The idea is new. So there has to be a "How the heck can I make practical use of this" list with every Web-Application. We regret that the clues are not obvious. But some users have put to use their imagination and have come up with great uses for Zoho Sheet. (Yeah, well there's this child-like excitement when someone does something as cool as these, you know)
That aside, here are some practical or everyday uses of Zoho Sheet:
(1) Help your child with seventh grade Geography homework on the topic of, say, "losses due to various natural disasters" while you are away from home.
(2) You can put up a comparison for the prices at various hotels in your city and share it with your friend who's planning to visit your city shortly. And to provide a visual clue, you can draw a chart instead of several rows of numbers. If you think, "What's good about that?", there's no need to have any spreadsheet installed on your (or your friend's) hard-disk. (Ok, this was inspired by Zoli's hotel room bill sheet)
(3) Manage your expenses every month. You can create a sheet for the first month allocating percentages for various expenses and clone the sheet for calculating the same for every month.
(4) Not-so-much-of-day-to-day-use, but an excellent example where complicated formulas were involved : Ismael Ghalimi's Navigation Log for Cross Country flights.
There are no limitations for day-to-day uses of Zoho Sheet. As with any web based service, it is entirely upto the user's needs and imagination. And as Mapz mentions, some thirty minutes of 'fun-work'.