In Google Reader:
Hit the "Options" gear in the top right corner and pick "Reader Settings".
Go to the "Send To" tab.
Pick the "Create a custom link" at the bottom of the page.
Name: Pinboard
URL: https://pinboard.in/add?url=${url}&title=${title} ${source})&tags=via:googlereader,via:${source}
Icon URL: http://pinboard.in/favicon.ico
Save.
To use, pick the "Send To" option on the item in Google Reader, and pick Pinboard. A new tab (or window, depending) will open, with a few things already filled in. This does require that you be logged in to Pinboard.
My options take the article title and the source as the title for your bookmark, and fill tags that specify that the bookmark is from Google Reader and whatever the feed source is. You may want to tweak that depending on your tagging scheme.
Crossposted to
Crossposted.