This morning he's hitting .417/.509/.635, good for first in the National League in batting average, on-base percentage, and runs scored despite having missed a Holliday-sized portion of April following his appendectomy. He's on pace for 46 doubles in just 127 games, and more runs scored than games played.
Holliday was 13% better in 2010 as a whole than he was in April that year, and that rate's held at six percent over his career. He's not going to keep doing it in 2011—it should be clear by now that the slow-starting portion of his body was the appendix, which was justly and swiftly removed after the diagnosis was made—but if he somehow maintained those 2010 splits this year he'd hit .461 with an OPS of 1.276 in the second half.
Which I'd be happy with, personally.