Two things about the theme - 1. It is somewhat odd that the revealer begins with a "PO" that is not in rebus form. 2. The clue of the revealer "39A: Mail conveniences ... or a hint to eight square in this puzzle" (POSTOFFICEBOXES) gives away too much. I don't think we had any of the rebus squares yet when we read this, but after reading it, you know what you're looking for, even if you don't get the answer right away.
On the brighter side, it's nice, I guess, that the rebuses are all contained in symmetrical long answers (although some critics find that sort of structure in a rebus puzzle also gives away too much, once you catch on to it).
I also enjoyed much in this puzzle. SHIITE (32A: Ayatollah Khomeini, e.g.) was good, GARTER (44A: Hose attachment) was tricky for me, but Frannie got it quickly. ASHE (18A: 26-Across of a North Carolina "-ville") (candidate for "Most Opaque Clue" of the year!) and E[PO]NYM (26A: See 16-Across) (gee, thanks) were tricky for both of us, but it eventually made sense. Wow, though. Really?
ANA (22A: Carrier to Tokyo) is unfamiliar, and MESNE (47A: Intermediate, in law) was too, even with some Latin. And even after looking it up, I'm still not certain I know whether or not it is related to "demesne." ITER (20A: Roman road), on the other hand, was a gimme. And speaking of legal matters, 56A: Legal borders? (ELS) totally got me today! They love that kind of clue, and I know it, and it still got me!
Lastly, I feel I must point out that "Wizard of Oz Week" continues today with TOTO (24D: Film pooch) (I originally tried "Asta").
Overall, I guess I liked it more than I didn't like it. You?