louieramos - 11:56 pm on Feb 20, 2012 (gmt 0)
Dont jump into the penalty conclusion yet. Google definitely had a major Algo update over the weekend or so, if your keywords have dropped in rankings it could be because your competitions have been working hard lately or it can be the cause of reindexing and backlink recount which has affected your rankings (your backlinks may have had less value now than before).
Keep an eye of your rankings in a regular basis too, it may just be a ranking fluctuation which happens a lot during Google algo update.
Also for those who suffered this main keyword dropped to bottom of page 1 or somewhere on page 2, do you notice what types of websites have climbed up on top of Page 1? Are they the strong brands on your niche? Are they aged sites on your niche? Can see any patterns?