So many excellent clues, so many excellent answers. I hardly know where to begin.
I'll start with the one I didn't like.
44A: Theoretical massless particle (Gluon). I had Quark first, then Prion. Before you go thinking I'm PDS (pretty damn smart), I'll confess that Don gave me all three. He wondered what I was doing during Physics. Never took it.
That's it. I pretty much loved them all.
15A: Formidable, as a task (Herculean). Got this with only the AN in place.
19A: Ladies in men's rooms? (pinups). We had this a few months ago. I remember Rex commenting about the ones in his bathroom. Or am I making that up?
33A: City where the Caesar salad was invented, 1924 (Tijuana). Who woulda thunk? I expected a nice Italian city when I had the NA in place. But I love the J there, especially since it starts off 34D: "Heart of the Tin Man" author (Jack Haley). Who didn't love the Tin Man?
35A: It may have two sides (entree). I had a story first. I love good wrong answers.
52A: U.S. chief justice, 1953-69 (Warren). John F. Kennedy's assassination was one of the defining moments of my life. If you're so inclined, here's where you can read about the Warren Commission Report.
53A: Skillfully switch topics (segue). One of my favorite words, so a definite gimme.
58A: Seafood restaurant annoyances (bones). Yeah, I hate having to see someone do the Heimlich maneuver when I'm eating.
21D: Field-specific vocabulary (lexicon). Another great word, and an X to boot! I guess 26A: Assessment on out-of-state purchases (use tax) will have to do.
30D: Heading for (en route to). It's just beautiful, and I like that it intersects segue.
52D: 1978-82 sitcom locale (WKRP). One of my all-time favorite shows. Johnny Fever reminded me of my brother-in-law, I thought Venus Flytrap was a riot, and I had an enormous crush on Sandy Travis. I also liked Bailey Quarters and thought I might name a daughter after her. Didn't...
How did it get to be 11:00! I'd better wrap this up. Don't forget to visit Orange's site (she's commenting from England), where the guest blogger du jour is John Farmer.
The weekend is almost here. Hang in there.