I signed up early to get on the waiting list for Google Spreadsheet so I could break it down here. As of this morning, Google officially invited me in to look at Google Spreadsheet, and so far, it works and looks great. It's fast and eerily mimics a full-blown desktop spreadsheet application such as Microsoft Excel. The menus are even very close to Excel.
The investor's question is this: Will Google Spreadsheet dent the revenues Microsoft receives from Excel, part of the Microsoft Office suite (that makes up a third of Microsoft's revenue)? Probably not at this time -- there are many corporate users that use too much of the Excel advanced functionality and won't leave it. But for the rest of us who need a straightforward spreadsheet application, and who would love to share "files" in real-time across the web, Google Spreadsheet may be the answer. Should MSFT shareholders run for the woods? I think not.
[Disclosure: I own MSFT shares as of 6-7-06]
Update 3:45pm CST: It looks like Google Spreadsheet *does* support multi-page "worksheets" -- they are just not turned on by default like in Microsoft Excel.