(1)  My sense is that the time and responsibility to do a blog is one reason many people drop out of the blogsphere. 

Perhaps there should be exit interviews done to determine why people drop out.  Would be an interesting survey.

I spend a lot of time focussing on "efficient blogging".  One article I wrote called "How to write an article in 20 minutes" has been read often.  A copy can be found at  http://ezinearticles.com/?How-To-Write-An-Article-In-20-Minutes&id=132380.

(2) [from Steven/Vaspers]: Michael Hyatt abandoned his Working Smart blog, due to time considerations, but valiantly found time to continue his From Where I Sit blog.

(3) here is a blog where the author feels the quality of the blog will suffer if she spreads herself too thin creatively, so Boobs Radley is going on haitus.