What have you been doing?
Have you been building links?
Have you been buying links?
How have you been internally linking to your content?
Are you publishing new content?
These are many of the fundamental questions you need to ask before you even start thinking of some sort of system-wide pattern.
A lot of people automatically think that if their rankings drop, then this means that everybody else's rankings have to go through a change.
9 times out of 10, the main reason why your rankings are dropping can be attributed to one of two things.
First, it's something that you're doing.
I know this is hard to swallow because a lot of people think that they're doing the right thing at the right time to produce the right effects.
And in many cases, they have a track record that supports their confidence.
The problem is just because things have been working out in the past doesn't automatically mean that things will continue to improve into the future.
You may be doing certain things that ultimately may be self-defeating.
So, look at what's going on from this perspective.
Are you sticking to Google's quality standards?
Are you looking to just come in with minimum standards?
Or, are you looking to truly deliver a superior visitor experience?
Sadly, the only person that can answer these honestly is you.
The second thing that could be going on is that even if you're doing things right, your competitors are doing things better.
Again, this is another bitter pill to swallow because a lot of people think that the search engine ranking game is very static.
They just think that they come in with a better equation or a better process.
Eventually, things will even out in the wash, and they will come out ahead.
If it only were that simple!
You have to understand that search engine optimization is like shooting at a moving target.
You're not just looking to improve your game, but you're also trying to keep ahead of your competitors who are equally trying to improve their game.
Do you see how this works?
Only after you have exhaustively asked and answered the questions above can you even start thinking about some sort of systemic change.
Personally, as far as my blog networks go, things are improving because I'm getting fewer random searches and are focused more on the sub-topics that I am actually targeting.
Other people's experiences may be different.