It's now available a new tool in Google Spreadsheet (and Docs too) called Complement.
Companies/Developers com create a complement, that is like a Excel add-ons, and integrate it into Spreadsheet.
I imagine how usefull would be to have a Wolfram Cloud complement, so, If I have access to it, I could use Cloud Deployed Formulas inside google spreadsheet.
I could create my own Cloud Function, that does complicated calc, database connections a so on, inside Mathematica, publish is to Wolfram Cloud, and easily use it um my Google Spreadsheet.
I believe It would be great for business users.