When it's 3am, and you have to get up at 8am, and this is your only free time this week to catch up on RSS feeds, and the unread items are 2540, and you don't want to spend more than, optimistically speaking, 30 minutes going through them, which posts gets killed and how?
1. After some time writing and reading blogs, you get pretty good at scanning things. You look for trigger keywords. You recognize reduntant posts that appear all over the net on a particular day and kill those.
2. Feeds with no content and a single link back to the blog die an ugly death. Chances are someone else on the reading list has reblogged your precious post and it will come up in its full beauty two scrolls down the road.
3. You speed through the blogs with the traditionally low gold-to-crap ratio (judged subjectively, of course). BoingBoing is a great read in general and publishes useful snippets every once in a while, but the chances that it will have something relevant to the topic are statistically very small.
4. Cute but meaningless headlines die rot in headline hell, just like email subject lines that carry nothing but an out-of-context "re:"
5. I'm still debating the value of ALL CAPS in headlines. Probably a thumb down, but it hasn't become too bad yet.