Love the five different area of investigation that you went over, great way to analyze and diagnosis the issue. I would also definitely agree doing a rankings comparison between the two time frames, and not only check what your Google ranking is, but also track the search volume for your keywords to see if it has fluctuated or gone down. Google Trends is a great tool for this as well, as one of your keywords that your ranking for may have just lost popularity online.
In the example below, Google’s organic results generated the most site traffic for the time period shown, but had a bounce rate that was greater than the site average. By contrast direct traffic generated fewer visits, but had a lower than average bounce rate. A page from another website, generated 5,946 visits but had a bounce rate 22.62 percent less than the site average.
I just joined digg a few minutes ago. I gotta tell you that I have been researching on this topic for several months now. By far the best article I have come across on traffic generation. It's one of the most comprehensive ones I've read. And includes a variety of sources which never struck me before. I'm a musician and I plan on starting a blog and uploading videos soon. This is really going to help me a lot and I'm gonna follow. :) I really like the idea of using sites like wiki, about.com, scribd etc...
Thank you Jayne, for doing all that voting and sharing, means the world to me! I am glad you saw some new ideas and looking at all the comments, I think I killed a really bug tree with this post, that is how many people want to print it out, lol. If at any point of time you get stuck with one of these, send me an e-mail, tweet, what ever and I will try to help you with extra ideas :)
The term “organic traffic” is used for referring to the visitors that land on your website as a result of unpaid (“organic”) search results. Organic traffic is the opposite of paid traffic, which defines the visits generated by paid ads. Visitors who are considered organic find your website after using a search engine like Google or Bing, so they are not “referred” by any other website.