Ouch! Have I been penalised in G Serps?

Something strange has happened to my rankings... it's so dramatic it looks like my site has been penalised?

I'm not sure if it's a site wide penalty, I haven't been measuring my ranking for any given keywords... maybe I should start?

I have noticed my search engine traffic as a whole, decline in the last week or so...

Possible things that could have hurt it?

1) There is a CJ link on a different page to download Skype (but that was always there)

2) I have other websites on the same IP address (unrelated)

3) The product that I reviewed on this page (it was an organic review - I bought it and I liked it) added a link back to my review from their own 'press summary' page.

I don't believe that any of these things are spammy, or worthy of a penalty. Could it be something else?

Also - any advice on how to measure your position in SERPS for certain keywords?

Thanks!