walkman - 12:28 pm on May 1, 2011 (gmt 0)
Too many tag pages are enough to do you in, although some sites I know have escaped that. Suppose I add [panda,thin content,penalty] as tags to this thread and for all three all you see is the same sentence with a slightly different title. Until Panda Google would have ignored one, now looks like they slam you with a penalty and drive you out of business.
The horrible news is that Google has no intention of taking changes in consideration for the time being. I made my changes on 2/25 and more 2-3 weeks later, just lost another 30% of traffic.