tedster - 11:11 pm on Feb 20, 2012 (gmt 0)

So far at least, there's no reason to think that Panda was run again or changed on February 18.

The discussion in our February Updates thread [webmasterworld.com] has several people spotting a significant ranking shift on February 18 - so that could point to some kind of algo update that also affected you.

However, seeing ALL your main keywords drop to Page 2 sounds a lot more like a manual penalty than an algo change.