Between trick-or-treating for parents and partying for singles, adult 18-49 usage was down 7% from 8-11 PM last night vs. last Wednesday. Most series posted week-to-week declines, many of them of the double-digit variety.

The X Factor had its first live show, introducing hosts Mario Lopez and Khloe Kardashian, whose bra-less appearance proved “very distracting” even for Simon Cowell. X Factor (2.6/8 in the fast nationals, 2.7 in the finals) was down 23% from the show’s last Wednesday episode. Vs. its first live show last fall, X Factor was down 40%. Some of the decline can be explained with the fact that X Factor was originally not scheduled to air Wednesday. The live show was added Monday, and not all programming guides/DVRs picked up the change. Fox still won the night in 18-49.

NBC’s 30 Rock (1.2/4 in 18-49, 3.6 million viewers) aired an original last night with even shorter notice than The X Factor — NBC only made the move Tuesday afternoon as part of a string Hurricane Sandy-related scheduling changes. The departing comedy held OK — flat with its last two airings in its regular Thursday 8 PM slot (30 Rock also tied last week’s episode of Animal Practice, which it replaced last night) and posting a season high in total viewers. Guys With Kids (1.4/4) also was flat with last week. Law & Order: SVU (1.7/5) was down 11% from last week’s 300th episode. Freshman Chicago Fire (1.5/4) was down 17% to a series low and last-place finish at 10 PM. (On the bright side, it was the only 10 PM show not to drop from the first to second half hour). Both Guys With Kids and Chicago Fire have orders for five extra scripts while NBC is mulling their future.

ABC’s Modern Family (4.1/12) was the highest-rated program in 18-49 last night  but it was down 16% from last week to a season low. The network’s No. 2 program of the night was evergreen It’s The Great Pumpkin, Charlie Brown (2.7/9) at 8 PM, which was up 17% from last year when it did not air on Halloween night. The 46-year-old cartoon won its 8-8:30 PM time slot and tied The X Factor. It was followed by newly picked up The Neighbors (1.8/6), which was down 10% from last week to a series low. At 9:30 PM, Suburgatory (2.4/7), was down 11% to a season low. Freshman Nashville (1.8/5), which is still awaiting word on backup scripts/episodes, was down 10% from last week to a series low.

CBS’ Survivor: Philippines (2.4/8) was down 14% from last week to log the franchise’s lowest rated regular telecast. Criminal Minds (2.9/8) was down 6%. CSI (2.3/7) was down a tenth from last week to a series low but topped the 10 PM hour by a wide margin. CBS won the night in total viewers.

On the CW, Arrow (3.4 million, 1.0 in 18-49) was down a tenth in both total viewers and 18-49. Supernatural (0.9 in 18-49) was the only series to post week-to-week gains last night, up 29%.