Apparently Google is attempting to replace Microsoft Office one app at a time. First it was Writely , a word processing app that runs on the web and can be used as a shared app. Now there's Google Spreadsheet  (wow, catchy name!), that is - surprise! - a spreadsheet app that runs on the web and can be used as a shared app.You have to have a gmail account  to use it, and you have to use one of the following browsers: IE 6.0+, Mozilla Firefox 1.0.7+, Mozilla 1.7.12+, or Netscape 7.2, 8.0. I bet you're thinking that pretty much covers the bases, huh? I tried it the first time out with Safari for the Mac and bottomed out. But once I switched to Firefox it was all good. Here's a screen shot:
It's another handy tool for libraries that don't want to or can't offer Microsoft Office to their users.
Another way to go is a service like ThinkFree , that offers online word processor, spreadsheet, and presentation software. Los Angeles Public Library  has opted for this route. You don't have to be a library to sign up for ThinkFree; an individual can sign up in just a minute or two (they'll need an active email address for verification purposes), and once they're signed in they have instant access to the three apps and a gigabyte of online storage (Google Spreasheet storage is part of your two gigabyte Google account's storage limit). Only downside: it runs on Java, which can be a problem for some libraries' public use machines.
Update on Google Spreadsheets: if you decide to share a spreadsheet with someone else, keep in mind that only one of you can edit the spreadsheet at a time (a pretty good safety measure, if you think about it!).