The rocket firing that Rosetta performed yesterday has targeted the spacecraft to within two kilometers of the planned position, an accuracy that the navigation team deems is good enough to cancel the final opportunity for a trajectory correction this morning. In fact, according to the Rosetta blog, the engineers seem to be almost jubilant over the accuracy of their targeting.
Some of you might be asking: if they had the chance to fix that last two kilometers, why not do it? My answer to you is that one of the most frequently quoted aphorisms I hear from spacecraft engineers is "better is the enemy of good enough." The current target position is only a quarter of a percent off from the target miss distance. They didn't say this but I assume that that's well within whatever tolerances they set when they were planning their science observations. Why take the risk of something going wrong with an unnecessary firing of the rockets? Let the spacecraft coast on in and do its work without any further fiddling.
Here's an updated animation of navigation camera images showing Steins getting brighter as Rosetta approaches.
We're now just about an hour away from closest approach!