Someone from the Microsoft Excel team should read this page.

Quoted: t is so inefficient to always send the most updated spreadsheet to-and-fro using email, and I tried the "Publish" feature that Excel provides, but others can only view and not edit and save the published spreadsheet. [Google Docs & Spreadsheets] has all the features I am looking for so I can now communicate, work, edit our spectacular trip to Alaska and have everyone's research for the trip saved, without worrying about having the spreadsheet overlapped by another user who is also working on the file at the same time.

I am trying to create a relatively simple chart in Excel 2007 -- and my machine is crawling. Going to try OpenOffice now.

Quoted: Charting Speed VERY SLOW
Excel 2003 created 100 charts in 8 seconds. Excel 2007 took almost four minutes to do the same task.

While I've adapted to the loss of menus in most Office apps, it's still a problem for me in Excel. This addin gives you back the classic menu, but it unfortunately doesn't support keyboard navigation of the menu.

Quoted: Can’t see the familiar menus and toolbars from previous versions of Microsoft Excel? Just download and install this software and you will see and enjoy the classic menu and toolbars of Excel 2003/XP in Excel 2007.

A comparison of Google Spreadsheet and EditGrid -- presented as an EditGrid spreadsheet.

More on Google spreadsheet. Very positive review....

Quoted: You can open XLS or CSV spreadsheets inside the tool and perform calculations, data sorting, run formulas — everything that you would expect from a solid spreadsheet app. There is also a marked emphasis on multi-user editing. Two or more users can view and edit a document at the same time. Users can be invited to view or edit a document, and Google Chat has been integrated into the application so that multiple users can offer input during the work session.

As far as i know, the fact that this is a shared, hosted, browser-accessible spreadsheet w/an invitation model differentiates it from Excel. I don't think this will stop people from buying Excel -- but it will probably create some stress at Microsoft.