Most feed readers let you import and export subscriptions using the OPML format. For Google Reader, you'll find this option in Settings > Import/Export.

But what happens when you need to export the feeds from a single folder so you can share them with a friend or upload them to a site? Google Reader lets you export the feeds from a folder:


http://www.google.com/reader/public/subscriptions/user/-/label/FOLDER
(you should replace FOLDER with the actual name of the folder)

Another way to share the subscriptions from a folder is to make it public and to use this link for the OPML file:

http://www.google.com/reader/public/subscriptions/user/USERID/label/FOLDER
(USERID can be obtained from the public page created by Google Reader)

This also works if someone shares with you the page of a public folder and you want to obtain the list of subscriptions from that folder. If I share with you my Googlers folder:

http://www.google.com/reader/shared/user/13577231804381328821/label/googlers

you can easily obtain the link to the corresponding OPML file by replacing shared with public/subscriptions:

http://www.google.com/reader/public/subscriptions/user/13577231804381328821/label/googlers