Around the start of the month I saw a drop in the serps. I'd been doing some new linkbuilding so wasn't surprised, I then saw that there'd been an update so thought it could be that too. Then today I logged into google webmaster tools and saw notifications from the start of the month that my site was returning lots of soft 404 error (redirects when google is expecting 404 error). I've always used a 404 to home redirect to make the most of this kind of traffic and it's never been an issue. I've removed that redirect and marked the issue as fixed in webmaster tools so I'll keep you posted on if my rankings return.