I have been wiped out on one of sites (ranking high in GG SERPS) by Fl and Jagger updates. The Florida update took 7 mos to recover from and the Jagger - who knows?
I'm not sure anyone has a 100% sure idea od what the factors causing the demise of long standing sites. I have heard many of "it's this - or that", but it's avery difficult task when you have no idea what's wrong and how to fix it.
I have accumulated about 30 new one ways in the past month from my PR4 blog and some ads on two related websites of PR6 & 5. My e-comm site that's hit again still has PR4 but I'm getting CREAMED by PR0 to PR2 sites (many were purchased from my wholesale distributor) and they're ugly - non SEO'ed (to a fault). In short they look like the last sites that GG would want to display?
I've gone through my site (1/2 actually) and corrected tons of pages with a validator, until I have 1/2 the HTML errors fixed. While doing this I found loads of pages with the same meta tags, on page text (they're almost identical items) as well as the HTML errors.
My question is how long do you think it woule be before any changes actually showed up in the SERPS? My home page (only) shows an up to date cache every day, but clicking on "cache" returns an older date on the cahed page than the listing which has today's date?
I think that my pages are being spidered, but no changes? It used to only take a few days "pre-jagger" to see an optimized page move in the SERPS. Now, I wait and wait but the new sections and prodct pages still have caches of 2 or 3 weeks old.
Sorry for the long post and thanks for reading!