Jim - agreed. Holding the event later in the year would certainly raise the chances that the course would be in better shape. However, I got the impression that Oakmont is typically in good shape by late April, and that this winter, which was particularly harsh, had a greater-than-normal impact on the course and the greens. And again, the rest of the course was in pretty good shape.
Nigel - based on the look of the aeration, I would guess that it was pretty recent. Maybe late March or even early April.
Michael - that's interesting. Though to be clear, this wasn't really an issue of the greens simply running slow. The issue was more with the overall condition of the green surfaces, which were aerated and sandy. The third green was probably equal parts grass and sand.
The strange part was that I played Fox Chapel and Pittsburgh Field Club the following day, and their greens were in much better shape. Field Club's greens were close to peak form, and Fox Chapel's were basically as good as it gets for April. Very odd.
With all that said, I do want to reiterate that the event was fantastic, that Oakmont is a great course, and that I am glad that I played. However, I am looking forward to going back in August and giving it another crack.