As you've no doubt heard by now, earlier today Readability expanded from a simple bookmarklet into a paid membership service with the goal of providing financial support to writers and publishers.
70% of all Readability membership fees go directly to writers and publishers. Every time a subscriber uses Readability on your site, a portion of that subscriber's fees are allocated to you.
In a roundabout way, the new service kind of urges--by incentivising--long-form writing over shorter, linked-list-type posts, which can only be a good thing.
Though not entirely novel (a few services have done something similar before), I think this one has a real shot at succeeding given the popularity of the Readability bookmarklet, and Instapaper, which will be coupled to the service. I'm excited(!), if a bit confused about the now-overlapping nature of Instapaper and Readability, but I guess the gist is that Instapaper will soon allow us to "pay" folks via Readability via Instapaper, or something. Marco says that in the near future Instapaper will be able to send reading logs to Readability (so authors can get paid based on your Instapaper activity) and that he's creating "Readability editions of the Instapaper [iOS apps]."
I doubt this new Readability model will truly take off until the Instapaper integration is complete, but it will be interesting to follow once the services are talking to each other. Early on it will be a perfect collaboration, but if Readability starts to get the kind of third-party integration Instapaper now enjoys, then it's not clear to me that both applications/services will be necessary (i.e., why wouldn't I use Readability to the exclusion of Instapaper?).
In any event, for the authors-getting-paid aspect to be economically viable, it probably is going to have to break into the mainstream (and yeah, it's hard to say when "free money" isn't economically viable, but you get the idea). My $5.00/month spread amongst the thousands of articles I read each month isn't going to amount to much for an individual author, even in the aggregate. If the service's popularity remains only with the web/information geeks, who tend to read more articles a month than the average person (by at least an order of magnitude), and from a greater number of sources, it's hard to see how the resulting sum can be significant. But, like I said, "free money."
(For those authors holding out hope that most other authors won't sign up to take their respective pieces of the pie (and thus leave more of the pie for everyone else), it doesn't quite work like that; the ability for publishers to get paid is retroactive. From the FAQ: "Readability keeps track of pages visited even before a publisher registers with us to view their statistics. If your site has garnered traffic to Readability, we're already earmarking money for you." I think that's great.)
Relatedly, if the service gets really popular, it's not hard to imagine authors/publishers making their sites slightly more difficult to read in an effort to compel readers to route their articles through Readability (thereby generating a micropayment).
That said, for the last couple of years I've routed everything through Readability, no matter how visually pleasing I find the site, or how easy it is to read its text. (I stuck with Readability even after Instapaper offered a similar bookmarklet.) I really don't care how good your site looks, etc.—I want a consistent reading experience no matter what I'm reading (mainly because, over time, it makes my reading more efficient).
I hope Readability eventually supports sending articles to Kindles. (These days if an article is longer than ~three paragraphs, I send it to my Kindle.) I've the perfect solution right now, but it gives no kickbacks to the authors. (Oddly, Readability was an integral part of one of the two solutions I used before the Chrome extension I just linked to, and which I may write up at some point because the solution is foolproof, beyond reliable and can't disappear at the whim of the developer.)
As for actually putting the Readability "button" here on this site, I'm not sure yet. I've long resisted an Instapaper button/link, mainly because, well, if a reader wants to Instapaper one of my articles he can just use his bookmarklet (believe me, he's not using Instapaper without the bookmarklet). I think the same will be true for Readability—I currently see no value in adding my own button/link.
(See also Anil Dash's thoughts; he, like Marco, is an advisor to the company.)