Varying your anchor text is pretty important. If suddenly a bunch of your anchor text is exactly the same, that is not natural.
Forum links will never kill your SERP. Please do remember that SERP depends on how many back links you have. John Chow has more than a million back links to his site.
okay... but have you try to check john chow SERP for his name as keyword? try it here it doesnt show john chow's blog, few days ago it happens to me too... but after I remove my my signature link... I got first position again... I guess this SERP is still mystery...
I guess this theory is possible, when I change signature, it will change bulk of dofollow link with same anchor link, and I guess google thinks that I buy some link...
try to generate a keyword that is related to your site then build more links, submit your links on all marketing avenues, it will improve your SERP do it everyday. forum posting will not affect your SERPs as a matter of fact forum posting will also help you get backlinks
no dear, not a kills SERP, in one condition Kills SERP, if you create wrong keyword links for your website.
I just had the same problem where my site disappeared from the SERPS for about a month after a serious amount of forum links and web 2.0 links where done. It turns out that it was just the google dance as my site was indexed the whole time. It reappeared in the SERPS today in the highest position it's ever been. Pheeew!
For an entire month? Although ultimately a good ending for you, I never see this droppage last anywhere near this long. Usually only days. But at least you got improvement.