There's a Greasemonkey script that sends articles you choose with a shortcut to InstaPaper. And afaik calibre has a recipe for instapaper, you can also add instapaper to mobipocket reader news without any hassle, works reliably. Though, the issue remains that if the article in GReader is only an abstract, not the whole thing, that is all you'll get, no extraction.
I'm sorry, I misremembered (early morning for me
). The script sends only the article url to instapaper, so you should get whole articles, even if there's only an abstract in Greader. Still, there sometimes is a problem with articles stretching over more pages.