How do you measure the quality?
If the blog network is a niche blog network, almost every blog will give more value than a a general blog. So I can believe there will be results with mere one blogpost.
But when it comes to general blog networks, one post doesn't help much. You need at least 5 contextual posts to see some decent ups in rankings.
There are only few providers who actually work on strong backlinking of these blogs (under networks). Fortuntaley, we do promote and build backlinks for our blogs in networks but still, 1 post from a a general blog cannot give noiceable results.
It would cost a lot if all 200-300 blogs of a network are build up with that high quality so they start giving results with 1 post. And if they do, contextual services would be way too costly. Hope all makes sense.
How I measure quality is irrelevant, what is important is how Google measures quality. And, unfortunately, much of that simply boils down to PageRank.
"Authority" is slowly becoming more important, but we can't easily "see" authority. PageRank is there for all the world to see and it is an important component of Authority.
You didn't get the sarcasm.. It was same.. It's all up to Google how it measures the quality. People are after PR.. and everybody knows that it's not difficult to purchase high PR domains and set up blogs.. And they will not actualy give any value if they're not maintained.
You are surely right. It's the authority that is considered and that gives value and help in rankings. And needles to say.. Authority comes with time and maintenance. We just need very strong and well-maintained blogs and networks.
Good post. Let's add some more tips...
Is the blog full of duplicate content?
Does the blog link to spammy sites in its blogroll?
Is it a high PR dropped domain?
You want to try and avoid all the above situtions.
Honestly speaking, when I hear the words "blog network" I look the other way. Most networks are automated to some degree, and automation translates to lack of quality.
The advice from Will in this thread is gold. The rest is up to you.