Have you looked at spreadsheetweb.com and calcfusion.com? The former seems mature, with plenty of real paying customers. The latter is new, and I guess they're still working on getting traction.
So when you say "convert a spreadsheet into a web app", it means many things to many people. Which is a real expectation management challenge!
In this case we are going to make it "cloud based" so there's no need to deploy anything. About the different kind of spreadsheet uses, the more use cases that we can found the better, also we are going to start with the more simple cases to reach a functioning product and then expand to the most complex ones.
This looks like real competition, what is good to validate that a market exists.
Thanks for the tip! I would look into them with more detail tonight