No, I haven't. Thanks for the tip. I will try that too.
How do they do it? The sheets are hosted an NumSum's servers right? NumSum is not OpenSource right?
I did try Zimbra's demo, but didn't like the approach; you can only embed a spreadsheet in a word document. I downloaded the code, but I am still experimenting with TrimSpreadsheets, so didn't have time to take a look at it.