One of my business sites ranked very high for several (to us) important kw phrases. With Penguin, we got knocked down to 9th place for the most important kw and were not to be found anywhere within the first three pages of results for the others.
As of last night, things began to improve. There was even more improvement by noon today:
Most important kw: 4th place
Second most important kw: 6th place
Third most important kw: 4th place
Fourth most important kw: 12th place
Sixth most important kw: 14th place
What we did:
1. Revised the menu to remove any suggestion of kw stuffing.
2. Rewrote the text on all pages and revised headlines and title tags, again to remove any possible kw stuffing, emphasis on natural language.
3. Added two new pages with fresh material, page filenames have keywords but are not hyphenated (other pages still have hyphens in file names)
I have not even looked at backlinks. To the best of my knowledge, there aren't any suspect links.
This is, I hope, a general improvement. With any luck, the site will continue to rise for its important kws and the improvement will be permanent. We shall see.
We also have a backup site which we've freshly tuned to stand in for the main site. This is a strategy we've had in place for years, one of those "What the heck are we gonna do is Google goes nuts?" provisions. If it turns out the main site fully recovers, I will detune the backup site to keep it out of the rankings.
Good luck to all.