Open Gmail's xls attachment through SpreadSheets.

Directly open the xls attachment of Gmail via SpreadSheets. Then you can save the file to your Docs account for easy access next time. You can also share this file with other colleagues, so there's no need to send this file back and forth as an attachment anymore.

I don't know why it's not possible to directly open a doc attachment with Docs yet. I believe that Google will definitely launch the same feature after some time.