Backup Google Reader Subscriptions

Simply go to Settings when logged in to Google Reader (upper right corner, you may get a drop down box so select "Reader Settings").

Select "Import/Export"
Click on "Export your subscriptions as an OPML file"
and Save this file to your harddrive.

You can import these feeds back into Google Reader (or any reader that reads OPML files) quite easily by selecting "Import your subscriptions" on this same page.

Be safe - backup.