Google just made an announcement that it will start a service that will allow users to create and share spreadsheets online.
See following news articles:
Google tests Web-based spreadsheet to organize data
Google to unveil spreadsheet program
Google Takes Aim at Excel
This is just a recent addition to a slew of other announcement of similar services by BaseCamp, ThinkFree and Writely (which was acquired by Google earlier this year). Although these services are not as full featured as MS Office, they do have everything necessary for most users.
With such office productivity services available to free online, do we still need Microsoft Office? -- No!
Update: Don't forget SUN's free OpenOffice.