Theme: Machine Language. All the clues are powers of 2: binary numbers, the way computers (or phone texters) communicate.
17A. 8?: HAD DINNER. Ate. (23 or 0000 1000 in binary)
26A. 2?: EXCESSIVELY. Too. (21 or 0000 0010)
50A. 1?: TOOK THE GOLD. Won. (20 or 0000 0001)
62A. 4?: IN FAVOR OF. For. (22 or 0000 0100)
39A. They're not literal, and this puzzle's title: FIGURES OF SPEECH. In math terms, numbers are "figures".
Hi  all, Al here on Thursday, Thursday, gotta get down on Thursday... Any  Rebecca Black fans? Oh, Friday, you say.  Well, I guess that's as close  as I'll ever get to being infamous.
I  found the puzzle today strangely slow going at first, but it wasn't  really all that hard, I just wasn't tuned in. The theme today was fairly  modern and enjoyably geeky, even though I refuse to abbreviate my own  text like that.  I would have liked to see the clues appear in numeric  or reverse numeric order though, to give it a third level of complexity,  but still pretty tricky.
ACROSS:
1. Not quite dry: DAMP.  Originally meant "a noxious vapor", the phrase "come in out of the  damp" was from the notion of the night air being bad and miasmatic  gasses arising from the soil.
5. "Battle Cry" author: URIS. Leon. A tale of a mixed-ethnic group of Marine enlistees coming together as a close-knit fighting unit.
9. Yippie name: ABBIE.  Hoffman. Youth International Party, anti-Vietnam protests, the Chicago  eight at first, then down to seven when Bobby Seale (Black Panthers  founder) was singled out and tried separately.
14. French darling: AMIE.
15. Reduce bit by bit: PARE.
16. Virginia political family: BYRDS. Harry Flood Byrd and son (Jr.).  I prefer the musical group.
19. "Back Stabbers" group, with "The": OJAYS.
20. Ones with dark-spotted faces: DICE.  Possibly my favorite clue for the puzzle today. You can always tell,  without looking or touching, what the bottom number on a six-sided die  is by subtracting the top from seven.
21. Annual draft org.: NBA. National Basketball Association.
23. 46th U.S. state: OKLA.homa.  Wolverine sings!
24. Nuevo __: Peruvian currency: SOL.  A lesson in run-away economics, the original currency, the inti became  so hyperinflated that new money had to be issued in 1991 at the rate of 1  sol = 1 million inti.
29. Dig up: UNEARTH.
31. "Ain't __ Sweet": SHE.  Some Beatles accompanied with 57A. Its full name means "jumping flea" in Hawaiian: UKE.
32. Pastures: LEAS.
33. Protein building block, for short: AMINO. Amino Acids. Haven't ever seen or heard it used in this shortened form.
36. Animal's stomach: MAW. Learn something new every day.  I used to think this word just meant a gaping mouth.
43. Happy hour order: ALE.  Ale, ale, the gang's all here!
44. Varnish resin: ELEMI.
45. When doubled, a fish: MAHI. I already think I know what JZB will say, half-baked, probably.
46. "Wheel of Fortune" purchase: AN I.
47. Contrary retort: DOES NOT. Playground rhetoric. The height of forensic capabilities.
55. Female rabbit: DOE.  Whale? Cow.  Elephant? Cow.  You'd think there would be more original  names for those.  At least a female swan is called something different, a  PEN.
56. Business head?: AGRI. A prefix clue.  Agribusiness  is a portmanteau of agriculture and business, referring to the range of  activities and disciplines encompassed by modern food production.
58. Raison d'__: ETRE. French, "reason or justification for existance". Kiss.
60. Insipid: BLAND.  Orig. from Latin blandus "mild, smooth, flattering, alluring".  Current meaning probably influenced by blasé.
66. It's slower than adagio: LENTO. Musical terms, Italian.
67. Somber genre: NOIR. French for black.
68. "Up in the Air" Oscar nominee Farmiga: VERA. With George Clooney, a movie about downsizing, apparently. Why anyone would go to see that is beyond me.
69. First noble gas discovered: ARGON. The third most common gas in the Earth's atmosphere, more common than carbon dioxide.
70. Lake Michigan city: GARY. Indiana.
71. Noted sin scene: EDEN. As in original sin.
DOWN:
1. Morse character: DAH. Or DIT, or even DOT.
2. Org. featuring seasonal flu information: AMA. American Medical Association. Vitamin D3, and probiotics for prevention.
3. Fifties, say: MIDDLE AGE.
4. Start to cure?: PEDI. Another prefix. A Pedicure is foot care.
5. After the current act: UP NEXT.
6. Operated: RAN.
7. Goddess of peace: IRENE.  Greek mythology.  Roman equivalent: PAX.
8. Some Bosnians: SERBS.
9. Donor classification letters: ABO.  Blood types, A, B, AB, and O, along with Rh+ and - are the most-known,  but actually Rh by itself has 50 types, where D, C, c, E, and e are the  main 5.  The + or minus only refers to the D form.  And ABO/Rh are only  two out of 30 blood group systems. It is much more complicated than you  can imagine and has its own discipline called immunohaematology.
10. Exclamation from Colonel Pickering: BY JOVE. Jovis Pater (Jupiter), also linked to a euphemistic shortening of Jehova.
11. Start to stop: BRAKE. As in "apply the". Caught me trying to think of a prefix at first.
12. Pastoral poem: IDYLL.  Latin idyllium, from Gk. eidyllion "a little picture". 
13. Common college admissions requirement: ESSAY. Latin exigere "test" 
18. Cake finisher: ICER.  Didn't get caught thinking about suffixes. There's a video game called  Portal that tells you: "the cake is a lie", which basically is a  metaphor for unkept promises made to you in an effort to get you to  finish some task.
22. Like-minded gps.: ASSNS. Groups, associations.
 
