The "Minus Thirty" Penalty?

[Hurri]

Hello everyone,

I just got my site rank #31 on its own domain name and bunch of keywords/phrases I usually watch were bumped from #1 to precisely #31. Those #2 through #10 are sort of all over the map but generally within the first 60 results.

Does anyone have some experience with this? What would the respectful audience here think a most likely reason for such penalty is? What do you suggest as the best strategy to fix this?

There has not been any major redesign recently, just routine adding pages here and there. Some unique, some syndicated industry-related content.

Thanks for any idea or comment!