As has been mentioned, I put this "improvement" down to the quality of opposition (and, to a lesser extent, Cork's return) rather than an actual improvement. At the end of the day, not every team has Van Persie or Jelavic in it.
I'm still not comfortable with the defence, and even less so with Gazzaniga. But against the likes of Swansea and QPR, you don't generally need a particularly special defence.
Think I'd be tempted to go back to Kelvin against Newcastle though (just not Boruc please; he looked unfit, a bit overweight, and just the whole signing of his stunk of desperate, and still does).