Unlike newer services including FriendFeed and AssetBar, Google Reader doesn't enable you to share items to your shared items link blog without first having an RSS feed subscription to the said site. But there is a work-around for this limitation, which lets you share an item without committing to any kind of long-term, or even short-term, relationship with the blog it came from.(See also: #4 in 10 Suggestions to Improve Google Reader from March '07)
To do so, you need to be using a feature in Google Reader's "Goodies" page, under your Settings, which they call "Subscribe as you surf". Essentially, you are adding a bookmark that with one click, prompts you to add an RSS-enabled site to your Google Reader.
I've personally added this bookmark to my Safari toolbar as "+GR", standing for "add to Google Reader", and click it whenever I find a must-subscribe site. But if you're in a gray area, and find a site that has a great article, but is one you don't think you'll be subscribing to, there's still a way to get it on your link blog.1. Click your new "Subscribe as you surf" bookmark.
Google Reader will show you what the feed will look like if you choose to subscribe, with the note "You are not subscribed to this feed yet" along with a "Subscribe" button.
2. Scroll to the item or items you want to share on your link blog.
3. Hit the share option.
Then you can exit out of the feed subscription window by clicking All Items, getting back to your feed reading, or get on with your life. Sure enough, even though you never did subscribe to that site, their item made its way to your link blog, to be shared with your Google friends, and services like ReadBurner.
Until Google finds a more direct way to share items from the Web directly to your link blog, this is a fairly simple work-around, one I've been using on occasion and will be trying to make more-frequent use of in the future.