We upgraded our http://https://www.zoho.com/docs/sheet.html? service couple of days back with some goodies like Multiple Sheets, AJAX, etc.
You can now have multiple sheets (as tabs at the bottom) in a single document (workbook). This is very useful for maintaining all related data in a single document. Your already imported spreadsheets will automatically show all the sheets now. You can insert / add / rename / delete sheets. You can also refer to a cell in another sheet in the document.
We have AJAX-fied the whole interface now. Loading a document / creating a new one is much smoother and faster now.
We have also created a Firefox extension to automatically go to Fullscreen mode whenever you visit https://www.zoho.com/docs/sheet.html?. Apart from that, we have done some fixes and enhancements.
Detailed information is available on our What’s New page.
We also acknowledge that some important features such as insert rows / columns are missing and we will be adding them in our next update.