The biggest change is the top left position of the first search result relative to the top left position of the document. In other words, the average scanning pattern has completely changed with the addition of a fixed side bar.
It will take a lot of people a long time to adjust and its effectiveness can't be judged by a couple of hours of usage. It's not unlikely to assume Google is very willing to take a slight hit in this area and win in the discoverability of their different ways to use Google, hopefully, eventually improving a person's overal searching efficiency.
Time will tell, but we all know Google tests these things through and through.