Check out this Google Spreadsheets - Sneak Peek. Personally I think this is cool. The technology is nothing hugely new, and the features of course don't match excel at all.... however, the number of users who use all of excels features, or really use anything more than basic spreadsheet capability, are probably pretty low. This, combined with the integration of google spreadsheets into gmail/gtalk/calendaring, etc etc, will make this something to watch anyway, especially with google's purchase of writely will make google something to (continue) watching.