My live Gentle Giant experience was the November 5, 1977 gig at the (now defunct) Palladium in New York City, during the "Missing Piece" tour. In addition to the concert's repertoire, my recollections from that show include Gary and Ray's comical gestures to each other, synched to their unpredictable rubato playing during the acoustic guitar duet in "Excerpts from Octopus", which got laughs and applause from the audience. Also memorable were Derek's frenetic arm movements calling attention to, or imitating, the other players during songs. This was especially amusing when, during Kerry's synthesizer solo in "Just the Same", Derek ran over to him, stood alongside, and pantomimed his double-keyboard playing. But I recall the audience's response being most demonstrative during Kerry's explosive vibes solo in "Funny Ways", which received thunderous cheers even before he finished it -- possibly the most vocal response to any of the songs that night.
In the middle of the show, I recall an equipment failure (or at least having that impression -- perhaps it was a tuning delay prior to "Funny Ways") that seemed to last indefinitely. It was apparently at that point that John delivered his monologue and stretched it out to keep the audience occupied during the extended delay. The friend who accompanied me recalls John's monologue as being about hemorrhoids, and says it's the only thing he remembers about that concert all these years later! Unfortunately, much of that New York audience was a tough crowd and expressed their impatience about the delay by heckling the stage, anxious to hear the music. But John appeared to take it in stride, even with humor -- and the band was rousingly applauded the moment they resumed their performance.
The strangest thing about that show was that the opening band was the straight-ahead rock-n-roll band Dr. Feelgood, who were continually booed by that audience of GG fans. (Those New York audiences!)
In looking back, it's amazing how much impact that concert had on me, even years later. Along with their live album, it crystallized GG as one of my favorite bands. It also inspired me to recreate their music as a project in my high school's electronic music class that year, to the bewilderment of my classmates, and to try to compose similar compositions. Their music was even a factor that year in my decision to pursue a music degree and attend music schools instead of a liberal arts college.