dickbaker - 11:28 pm on Mar 3, 2011 (gmt 0)
Sites that are narrowly tailored have been faring well (all other factors considered) for quite some time. Search phrases I tracked last summer showed that sites that were about the search phrase only could be out sites with more traffic or links.
It's tempting to build some focused sites for products I already sell, but have lost ranking for. As Jane_Doe said, it levels out some of these updates.