One tip, to solve the "chicken and egg" problem of getting a good garden going while still consuming current levels of information, allow the user to choose to include some of those "low quality" sources as well.
For example, right now the vast majority of my info comes from HN and Reddit, both from links and comments. Ideally I'd be able to subscribe the service and keep getting all that info, then as I slowly build up my own more personalized, curated sources I could slowly start to remove the low-quality sources. I think if you could make this a pretty frictionless process you'd have a winner.
Most of what the OP describes could probably be done pretty easily in yahoo pipes. Especially if it could call out to external services for ML recommendations.
I'm just starting to use it for most of my content consumption, so that I have a nice corpus of data about my preferences. The goal is to eventually develop a predictive model to start filtering content with...
I've got too much else to work on currently, but I'd love to see what you come up with :).
(edit: to see your shared items go to http://www.google.com/reader/shared/username)
I also used Bayesian classification to determine which articles were ones you were more likely to be interested in reading.
: the marketing pages are still online for this ancient piece of code: http://blazingthings.com/zestynews/tour1.html
: I created the TurboGears web framework while creating Zesty News, and ultimately decided to pursue the framework rather than Zesty News.
In addition, your system seems to be more about automatically finding content, whereas the OP's system is much more manual and curated by the user.
I signed up for your beta list because I actually think your idea is interesting, but I think they solve two different problems.
Subscribing to Hacker News I have figured out it being simply parsing the RSS feed to generate links. How do I go about doing it for the other types of feeds? Does Twitter and Google+ feeds require integration with their individual APIs? Any help is greatly appreciated!
Use Pipes to aggregate, filter, de-dupe, summarize, tag, and then feed your Reader.