As Pedestrian explains, the day is traditionally celebrated when one's local marja declares that he has seen the crescent of the new moon. This year, however, Khamenei took the unordinary step of preempting Iran's high clerics and declaring that he had seen the new moon. For their part, Grand Ayotollahs Montazeri, Sanei, Bayat Zanjani, Mousavi Ardebili and Safi Golpayghani all came out to publicaly state that they had not seen the new moon and that it would only appear the following day.
By challenging the Supreme Leader, the Grand Ayatollahs effectively created a separate (read: Green-friendly) eid holiday, thereby further reducing Khamenei's legitimacy in the eyes of the country's clerical establishment. Not surprisingly, Mowjcamp reported soon thereafter that Montazeri had been forced to cancel his eid prayer, as to not have it surpass the Supreme Leader's.
When eid finally arrived, many were surprised to see that Rafsanjani was in attendance at Khamenei's service. Some are speculating that a deal may have been struck, assuring the powerful Rafsanjani would be present and thereby giving the Supreme Leader's image a much-needed boost. For his part, Khamenei declared in his sermon that any evidence arising from in-court confessions could not be used against third parties. This would, in effect, give Rafsanjani and members of his family “immunity” from prosecution. (Several of his children have already been briefly and temporarily detained.)
It remains far from certain that such a "deal" was made, however, and such speculation should be taken with a grain of salt. Agha Bahman, for one, notes (and Pedestrian translates) that Rafsanjani's presence or absence at Khamenei-led events in the months following the election has been deliberate rather methodical:
In the past three months, Rafsanjani did not attend two events which he was expected to attend: the two inauguration ceremonies. Both of these events had to do with Ahmadinejad and giving legitimacy to his government, [and this was something that Rafsanjani did not want to do. Notice, just a few days after those ceremonies, he went to the goodbye and welcoming ceremonies for Shahroudi and Sadeq Larijani, the previous and current head of the judiciary.
The judiciary head is appointed by the leader, and if Rafsanjani had reached a point where he wasn’t willing to pray behind the leader, he shouldn’t have showed up there either. Rafsanjani also did not attend the two Friday prayers led by the leader, [but] unless Rafsanjani was the prayer leader, he never attended the prayer - no matter who it was leading it.
It seems that if anything, Rafsanjani's bargaining power vis-a-vis Khamenei increased following Quds day. It would be surprising if he would accept such a meager concession from the Supreme Leader in exchange for his still-questionable "support."