Who knows if it'll be any good, but Google will be testing a new web-based spreadsheet. You will be able to download the sheets to your computer and edit them, and also invite other users to sign in and work on the web saved sheets. Apparently they will also be looking to do the same for word processing.
I don't know if this idea will work, after all, there are a ton of different functions one can use in Excel, and it's not clear if many of them will be available on the web-based spreadsheet. But one thing is clear to me, and that is that Google is really on the forefront of innovation. Yahoo! and Microsoft seem to be lagging behind in their web services. GMail forced the competing web-based email services to offer more space and Google Maps forced Yahoo and Microsoft to update their maps programs. Then the Google Desktop software allows you to search documents on your PC better than anything included with Windows, and has little Gadgets that are essentially duplicates of the Yahoo Widgets.
The innovation at Google is pretty cool. They're coming up with new ways to do "old" things (like Calendar) or new things altogether. Google Spreadsheets is just another example.