It took me a while to get the Send To Instapaper feature to work. First of all it's only part of the paid version. Not a big deal. Then I wasn't reading your tip completely, and thus couldn't ever get the shortcut screen shown here to come up . "Simply tap and hold A LINK to see the shortcut menu." [emphasis mine] Tapping & holding a tweet doesn't do it, the link is the important thing.

Thanks, now that I've figured it out it's very cool.