That being said, I'm still not sure how I feel about the need for an actual client. Do we really need an entire other app for Instapaper? I'm sure some people will love it, but I'm not so sure that I am one of them. Maybe it's because I like opening up my saved articles in new tabs and reading them on the actual writer's website anyway. I seldom use the "Text" feature (except for when I use the iOS apps, in which case that's pretty much all I use).
Oh, and you can only use the app (with Instapaper — it works with Read It Later too) if you are a paying Instapaper subscriber ($1 a month).
Basically, here's hoping that Marco gets around to updating the website interface sometime in the near future.