crobb305 - 7:52 pm on Feb 2, 2012 (gmt 0)
Jan 2: Noticed that many of my pages somehow lost their correct H1, title and meta tags. Fixed this.
I wonder if this is tied to your problem. I also experienced significant drops in January after making tweaks over the holidays, in fact I was going to make a post about it. I suspect there is limited flexibility with how much tweaking we can do to H1/title, particularly adding/removing/adding back, etc?
On a different note, I also see G returning unintended pages for some of my phrases, perhaps the second or third most relevant, as you reported.