serpsup - 12:10 am on Jul 14, 2012 (gmt 0)
@timwilliams - I am also seeing very different sets of users coming in from Google, so you are not alone. For once, yesterday finally helped me and conversions were up, back to normal for the first part of today, and seem to be picking up in the past few hrs. In addition to sales, I notice a big difference in the user metrics such as time on site, bounce rate, etc.
My theory is Google shifts the SERPs around and sometimes you end up with better keywords driving traffic than others. I get mostly long tail since my site was hit by Panda 1.0 so it is not as easy to notice the good traffic from the bad but maybe one of these days I'll actually figure out a way to trend this data better.
Note: I am US ecommerce affiliate site, hit by Panda 1.0, and have been making a TON of changes since I was hit by Panda so take all this into consideration w/ my comments above. Since I was hit by Panda my keyword set is in constant motion and I too have noticed trends of recurring sets of keywords that come and go in phases.