Most of the great blogs that I visit are all done altruistically. They are well maintained, post useful information, and very rarely waste my time. They also require a huge amount of effort on the part of the blogger because they really have to do work to gather and present interesting and useful information for their readers.
What a lot of the press has referred to as blogging is "narcissistic." Instead of coming up with interesting information and vetting it for their readers they mostly just spew whatever thoughts they had that day onto the page. It doesn't take a huge amount of effort, but the signal to noise ratio is also very low.
With the rise of Facebook and Twitter, narcissistic blogging can happen more in the sphere you want it (your friend group). Narcissistic bloggers are usually doing it for attention and their friends' and acquaintances' attention is more important than strangers'.
Altruistic bloggers, on the other hand, have useful information to present so they want to present it to as large an audience as possible. While I think we'll see more narcissistic bloggers moving to Facebook and Twitter in the future, hopefully the altruistic bloggers will continue putting the time in for the public.