Ashley - be carefull when presenting content to users/bots - if its auto IP based you can run into issues with bots as they tend to be US based. So I'd check up on that.

It doesnt sound like you've been penalized - if you had been you certainly wouldnt rank top for "seo best practice", one thought is whilst you've discounted the migration effect, it could be related to that.

@Dan

I just searched & you're no longer showing anywhere in the top 100 for 'seo best practice'.

Oh great...! If you look through the results then any human could clearly tell you this just isn't right? A bunch of low-ish quality sites who link to us as the source content and we're nowhere to be found? Google, if not penalising us, has clearly severely downgraded our domain...

Interestingly a search on 'Econsultancy SEO best practice guide' returns our homepage, not the SEO guide page which it did this morning. Suggests to me that Google isn't liking our geo-targeting for this page...

Is it possible that doing that has altered your linking profile to such an extent that the site is being 'reevaluated' by google?

Yes, possible. Though I doubt it would cause this dramatic an effect. But it certainly looks like we've been demoted whilst Google 'figures stuff out'?

Perhaps someone's pointed a bunch of links at you from really bad sites.

Reckon this is unlikely.. Why would they bother? Would it really work? We've got over 300,000 'good' links so they'd need a lot and to do it that quickly would sure 'trip' Google. Unless Twitter is bad - we've had a lot of links from Twitter recently!

A pair of googlebots have crawled you from different geolocations, noticed you're serving different content to each of them, and nobbled you.

Could be this but a bunch of other SEOs swear blind that Google *only* crawls from the USA so would see our US version.

Fundamentally we don't *want* to be doing anything for Google's sake. We're doing all this only for our users' sake which is, indeed, what Google always advocate. Which is why I'd really like someone from Google to reply and stop us running around guessing and potentially undoing something that is fine in the first place!

Probably Gary Barlow's fault though, you're right.

@Daniel - the domain changes were in December 2008 so around 4 months ago.

You're right that there is still content in Google under the old domain and I don't know quite why Google is "holding onto" those results - if you click on the results then they should go through to either a 404 or the new site? And, in the latter case, using a 301 redirect. So why are they still there... I'm not sure.

Our rankings have got significantly worse today - we don't rank on any of our big reports at all. In fact the only search result I can find is our homepage. 

Which tells me *something bad* has happened. Still the only thing I think we could be penalised for is us using geo-targeted personalisation on some of our reports pages (see discussion at http://www.google.com/support/forum/p/Webmasters/thread?tid=4d7ef2450a000e2d&hl=en for details).

I still maintain we're doing the right thing for users but try telling that to Google. Until Google can confirm definitively we're guessing. And we're starting to make changes to the site to try and keep Google happy (which are guesses) as opposed to focusing on our users. Which is annoying and supposedly not what Google would urge us do.

@Dan No - Webmaster Tools all looks fine. I've submitted a Reconsideration Request but no idea if/when they might get back on that.

Ashley: I think you are right, that the problem is a duplicate content penalty caused by the personalisation of pages.  You are supposed to choose a 'canonical' version of every page and then block google from all the duplicate versions by using robots.txt or meta tag.  This way you can be sure that google isn't seeing two versions of the same page.  It shouldn't be difficult to implement and I think theres no thing to lose by trying it.

I still think Google has a long way to go in improving it's algorithm, because I know of many sites that are having this kind of problem.  They have tons of quality content but they are not ranking well, whereas some frames-based site with about 6 pages of lame content that hasn't been updated for 8 years ranks #1.