This happens a lot to technical people -- it's that neverending consumption of knowledge thing. What I've done that's helped me more than anything is to recognize the wheat from the chaff - that there's such a thing as quality of information, and that quality trumps relevancy. Wikipedia often has valuable information that is worth spending a few hours on, even if it's French kings.

Slashdot has high relevancy (to my job) but low quality, so I have a subscription to Ars Technica. No on-page comments, better writing, better summaries, less sensationalism. I get the same info (they have a huge coverage overlap), but the quality is different. Digg has zero relevancy and zero quality. So Digg and Slashdot don't make it on to Google Reader, and for any subscription, when I find myself marking "mark all as read" more often than not, that subscription goes.

-josh