A few days after this my website started going downhill in the serps.
Chrisv sorry to hear about this... Hope this means that I am going to be seeing the opposite effect :)
Regarding the other 10-15 projects that I closely monitor, only my new EMD eshop is struggling for its EMD keyword, but traffic stats are up.
The others show things like 200%, 400%, 120%, etc. increase from April last year, so haven't felt either the Panda or the Penguin updates.
I think what paid off for my clients is great content written for the user and from a user (as opposed to from an SEO) and only editorial links from highly relevant industry places, along with some guidelines for the PR team (for the big brands) to include links on press releases and never copy text from the site.
Also "below the radar" SEO changes on the site... Always in conjunction with the copywriters and the other staff involved.
Despite seeing loads of spam in the SERPs, the sites seem to have survived ok. I think "amateur" looking SEO pays off big time. Things like no keyword stuffed titles, keyword density around what the author thinks people would search (after some training of course) and generally making the site look natural and not showcase your SEO skills.
And I am talking about long-term domination. 5 years on still Google traffic is up (year on year), even on sites without that many content updates.
Especially the update where you rank for keywords not included in your copy has proven very beneficial and has made things easier for me regarding On-Page issues.