Well, a lot of these people have never posted or lost interest and stopped posting. So they really don't create much of a reading burden. If everyone decided to start posting 5 times a day I would be in trouble, but seems pretty unlikely.

Mostly, it was just hard to come up wityh something to say about someone I friended due to a message board that I barely knew them on over a year ago and who has never used their journal.

If I just unfriended all of the LiveJournal support and development related communities, I would probably never have to go back a page to read all of my friends entries unless I've been on vacation. (changelog has been especially high-traffic lately since they've almost completed the new style system.)