Web as a OS? not yet!

I recently start using Google Spreadsheet and first, I was very surprised it can give me similar user experience as the MS Office, like ctrl+C and ctrl+p; But after I use it more, I found Google Spreadsheet is far more surfficient to challenge MS Office.
1) The reason I use Google Spreadsheet is certianly for sharing. However, after I invite my friend to edit, they kept complaining to me on MSN that Google Spreadsheet shows them "It seems you don't have access right to this document". Then after some time, they can see the sheet. After many time, I finally figure out that the reason is because when my friend accessed the sheet, I am still working on it. We two can't edit the sheet at the same time. However, the error message is so confusing. This should be something Google at lease can do. Just let the other user view only while someone is editing the sheet.

2) Sometime Google Spreadsheet gave me errors like "It seems that you have edited this sheet during offline" and gave me two choices, "either discard the offline edit or view only". Again, I don't understand what the second option means.

Beside Google Spreadsheet, I have been using Google personalized home page for a while. I start feeling I am still using My Yahoo. No revolution, Just Buzz!