Google has added a new feature to their web based email system, Gmail, the ability to import to Google Spreadsheets any Excel spreadsheet received as an attachment in an email.
When you receive an Excel spreadsheet as an attachment in Gmail, a new option will appear next to "View as HTML" and "Download": "Open in Google Spreadsheets". If you click on that link, the file will be imported to Google Docs & Spreadsheets and you can start editing it. This is useful if you don't have Microsoft Office, OpenOffice or other office suite. You can also invite the person who sent that document to Google Docs & Spreadsheets, so you don't have to email the new version of the spreadsheet. You can use the mail that contained the attachment as a bookmark: the next time you click on "Open in Google Spreadsheets", a dialog will offer to open the existing copy.
This is another step from Google from their process to integrate all the tools they have created so far into a big Google Platform.