Robert Charlton - I'm not sure if too many links from Pinterest is the issue as all of them are nofollowed anyway. Currently I have around 10,000 backlinks from Pinterest, but I've only pinned a little over 2,000 images myself and that includes my repinning other people's images to my boards. I pinned one new image from my site yesterday that had 38 repins in a half hour...so that negates your theory about the content not being compelling enough.
You are correct though that my backlink profile is probably not diversified enough. I currently only have one other site providing more backlinks than Pinterest and that's a Russian blog site called 'mylivepage'...not sure if I even want all those Russian links!
I am very late to the social media party, and never had a blog because I didn't want to divert even more time away from the core of my business to write blog posts. Since Panda I see that all the top spots are crowded with low quality pages of syndicated content that seems to change on a daily basis, and the few remaining small businesses all have a strong blogs and huge social media presence. So I've diverted my attention away from the whims of Google and I'm now focusing on social media. Within a week of turning on Facebook ads I had an $1,800 order from a customer who beamed that she found me on Facebook. Can't say the same for Google ads, which cost 20X more and produce almost no leads or business whatsoever...and never have in the 7 years that I have tried them on and off.
Why? Perhaps because I am in a visual business, and on Facebook people can see the pretty pictures instead of just another text link? Friends of friends carry much more weight than a page crowded with ever more links trying to grab attention. That's why Google is desperately pushing Google+, and not the other way around. I would gladly spend a fortune on Google ads and forget worrying about SEO entirely if I saw a good return, but sadly I just don't.