dickbaker - 10:30 pm on May 2, 2010 (gmt 0)
Traffic to my site is off over 30% from March and down even more from last year. Having tested a bunch of key phrases and seen them slide in rank a few spots, I attributed the drop in traffic to the update.
However, the percentage of referrals from Google as a percentage of all referrers has remained unchanged or even gone up a point or two. Ditto for Bing, Yahoo and direct traffic. So it would seem that the drop in traffic is seasonal or niche-related.
If the percentage is unchanged, though, and main phrases such as "Acme widgets" have dropped in rank, that would mean that long tail phrases must have increased in rank.