4/15 seems to be the day. It's not just us we have talked to our suppliers and they cite that day too as when business pace changed. Whatever the cause its not just the search results I agree. The question is did the events at the marathon cause search behavior changes or was it something else? It is really odd but that seems to be the date that all different types of businesses noticed a change.
Google has added to the trouble by heavily bumping their paid results. I'm a little disappointed in the 60-70% real estate given for ads on many profit searches. They're starting to look like a directory more than a natural search engine.