A large number of my RSS feeds are subscribed exactly for the purpose of skiming. They fall into a couple catagories:

* Sources of headline level knowledge - basically things I note just to keep my brain up on things to search for later should they become relevant. Also useful for the occasional underreported story I'm actually interested in.

* Light reading - there are a ton of comics and blogs that I enjoy for light reading at the bus stop or whatever, enjoyable but really just skimming, or other not-deep forms of reading

* Feeds with occasional good content - basically i don't care about most of these articles, but they provide a gem often enough that I should monitor their content.

And various combinations of these. Product blogs or project blogs are good examples of this. I want to know when the new version is out. I don't care how they solved problem X, but the problem Y writeup may really interest me.

Spot-on on all points. Also of note, there are "noisy" pre-aggregated feeds out there which are useful for discovery of new authors or blogs, but have content wildly varying in quality or interest.