Why did I get a penalty even if I had some unique content?

[norwegianguy]

Our site has had top national niche rankings in 5+ years, but suddenly all rankings were gone due to an unknown penalty. The site has about 300+ articles.

Is there any way to find out the penalty cause?

1) One (and only one) article delivered by a lazy freelancer (now fired!) that obviously was translated by Google Translate into our language
=> Theory: Google translate penalty

2) Articles have unique content with lots of non-spam comments, but subpages had auto-generated content like news from Google, images from MSN and videos from YouTube (before they got their "add content" / widget services). I consicdered this "cool" at the time, but it should have probabley been "noindex" content.
=> Theory: Automated content penalty

3) Design: Doesn't look too professional.
=> Theory: Human reviewer from Google didn't like the site

What would you do?
-Create a new site and re-publish the uniqie connent
-Forget about it; move forward to new niches
-Remove the old auto generated content and ask Google to review my site
-Other?(Thanks for any suggestions!)

[aristotle]

My suggestion is to clean up everything you can identify as a possible problem, then submit a reconsideration request. If that doesn't work, then you can still look at the other options you mentioned.

[tedster]

Also look for any possible hacks to your server [webmasterworld.com]. (Are you using Wordpress, by any chance? If so, look twice as hard and make sure your software is up to date and patched.)

My take is that only your #2 idea has any significant chance of being involved. One plagiarized article will not do it. And a non-professional design isn't likely to do it, either.

[tangor]

Do all the above. Meanwhile, push Bing and Yahoo.

Are you sure it is a penalty? Could it simply be there are THAT many sites in the same niche and you finally got knocked off your perch? (I tend to believe that more than any "penalty"). It's hubris to believe one's site is that much better than millions of others in the same niche. Serious.

Sometimes starting over with new (that also means new DNS etc.) will get G's motor running again. Anything that links or smells like your initial site will not benefit. Just my 4.5 cents (inflation)

[Robert Charlton]

...but subpages had auto-generated content...

What percentage of pages on your site are we talking about?

[norwegianguy]

Hacks: CMS is built in-house, but I will definately look more into the deeper hacking issues (cloaking / dns).

Penalty or not: Drop in serps was pretty sudden, from one week to the other, typically from pos 1/2/3 to page 2 or 3 for most phrases. Competition is national only, there's still just a handful of competitors with matching content quality. I have a hard time to believe we've been out-googled by the others. Serps are all fine both in Bing and Yahoo.

Auto-generated content percentage: I would estimate 20%, though most of these also have user generated content (comments).

Right before the drop, the site was updated with lots of new articles. Another theory is that the G algo is tweaked to look for bad smell in new content more than old. Could that be the case?

Thanks to you all for replies and suggestions!

[norwegianguy]

Update: I removed all pages with auto-generated content from the navigation, and within about 10 days, the good old rankings were back. I didn't even submit a reconsideration request since I wanted to redesign the site first.

Thanks for useful advise that helped me get my rankings back.