I just pushed a tiny little update to the GReader Instapaper extension. It shortens the default speed at which the notifications disappear, and adds a settings item in preferences so you can adjust it if you want to. I think the 1300ms delay is a pretty good one, it was 5000 before (and everyone complained). All better.
I cleaned up a few loose ends, fixed some error messages, general housekeeping. However, I’m still stuck as to how to tell when a post to Instapaper fails. I’m unable to get a response code from the async post, so all I can really tell is that there was a response. I can’t tell if it was good or bad. So… the notification will pretty much always tell you it was a success. If your articles aren’t showing up in Instapaper, check your username and password in the settings and try again.
I doubt I’ll push much further on this, given that the Instapaper bookmarklet does a fine job with Google Reader, and you can trigger it with a ⌘-# if it’s in your bookmarks bar, # being the position of the bookmarklet in the bar, from 1-9.