...it seems that, Google SERP changes isn't the only reason for a huge drop in website traffic. Over at the Google Groups, JohnMu of Google has stated that, the site traffic drop can also occur due to the quality of links, that aren't upto the expectations of Google.

Find below some excerpts from the Google Groups Post: (Bold quotes are where JohnMu gives his opinions)

Could be a problem with the bot accessing the page/site/server.

Can you check the logs/host to ensure the site was fine at that time?

Hi Dave and welcome to the groups!

Looking at your site, it might be that one issue could be that links
pointing to parts of your site are not valued in the same way that
they used to be.

Hi John,

Interesting response, so I have had my links devalued, that sucks as
they are all organic and good links as far as I know.

Is this temporary or permanent and will future links count?

Thanks.

We dont use that anymore, a SEO company we used put us in it and even
though we have been removed months ago after finding out the sites
displaying the ads seem to take months to stop showing.

We were told all the sites ranking for 'loans' use it and it was ok,
we soon decided otherwise.

They still manage to rank for one of the webs most competitive terms
just fine however.

Hi Dave

If you know that a previous SEO company used methods which are against
our Webmaster Guidelines, I think it would be important to mention
this in a reconsideration request (as well as doing whatever is
required to make sure that these issues no longer exist). It would
make sense to provide enough details and of course to be honest in
that regard. That would be my suggestion, if you haven't already done so.

Del.icio.us

Digg

Reddit

Furl