Not ready for prime time!
I was trying to use it yesterday for compiling insurance readjustments for my Katrina losses. I liked the idea that I could have the spreadsheet on my desktop and be able to take my laptop out to the house and wherever I did the entries the other would update as well.
Nice concept, but there is a serious problem. I had it set to auto-save and it would confirm the saved data. I could go to the window I had left open on the other computer and see that it had indeed updated without user manually refreshing. Nice. Unfortunately it will occasionally pop up a window saying you have lost connnection to the server and it is attempting to reconnect (which it never does). On the popup you have 2 buttons, Refresh and lose saved data (wherever it had decided to stop auto-saving, which is well before the popup) or go into View Mode. View Mode will bring up the data you were working on and the only way to save it is to open another window, log back into Spreadsheets and copy and paste all the entries individually from the View window back into the spreadsheet.
I tried the Refresh button the 3rd time it happened and that would bring up an error saying it couldn't connect to Google and try again in 30 seconds, which I tried a dozen times. At this point I was through with Google Spreadsheets and exported what data I had remaining to my desktop to use on a local spreadsheet program.
Lesson learned: Don't use Google Spreadsheets except for small amounts of data, or on anything terribly important.
