There are, I believe, a rare few ideas in the world that are truly new.
Most things people come up with are a twisted version of something that already exists. That is, more or less, the definition of "innovation", isn't it?
Take an existing idea, tweak it enough to brand it your own and you have an "original". Find a way to hold it up as "the first" or to, one way or another, be "number one" and you have something bankable.
In a similar vein, the lifeblood of the blogosphere is borrowing ideas that you see being used by other bogospherians.
Coining a truly new term, as I have here to replace bloggers with blogspherians may fall flat simply because it takes explaining. You could say to someone that you are a blogger, meaning that you maintain a blog. But to be a resident of the blogosphere makes you a blogospherian. Pass it on.
Now, back to the point. If you see a blog that you think is a good idea, which has all but been abandoned, I do not see it as an ethical dilemma to pick up the ball and run with it.
I expect to be following-up on this one at another time.