I'm still trying to figure out what happened to my site's rankings about a year ago, but I don't think it was due to bad linking - at least I don't think it was. I never got a notification from Google for suspicious link building, and I only had about 500 links on a domain that I had owned for about 4 years. So I guess my questions are: 1) Will Google let you know if they downrank you due to "bad" link building? 2) How many backlinks is suspicious? Are we talking hundreds, or thousands, or tens of thousands?