Plot: Little vignettes are interspersed with a USO show at the 4077th, including a series of practical jokes played by Frank on Hawkeye, and a homeward-bound dentist who is paranoid that something will happen to him before he can get home.
I love it that Frank actually gets back at Hawkeye a little in the episode. (Although I want to know how he managed to make the showers do that!) Hawkeye deserved everything he got, and it's nice to Frank fight back for once. Even if Hawkeye did get him in the end, it's more even, and this is one of the few episodes where Frank gets to be treated like a human being.
Other plots include Henry worried about his wife who's having their third child, a boy -- it's a little more poignant, knowing that Henry will never get home to meet him. Trapper worries about an difficult case which Margaret helps him on, leading Hawkeye to speculate about the two of them. The patient recovers, thanks to a little help from Father Mulcahy, who had been worrying about his effectiveness.
I always loved Father Mulcahy's comment after the patient awoke: "It's not supposed to work that way, you know."
Captain Kaplan, the dentist who's going home, was previously seen in "Major Fred C. Dobbs".
Henry says the obstetrician who's delivering his wife's baby, could do it with his eyes shut. Radar remarks that that's how he'd do it. He's not kidding, later in the series that's pretty much how he helps Hawkeye deliver the South Korean mother's child.
A nit: Henry refers to his wife as Mildred. In other episodes, her name is Lorraine.
Isn't Colonel Potter's wife's name Mildred? Hmmmm.... I sense some hanky panky going on...
Yeah, but judging from Nancy Sue Parker, the girl that Henry had an affair with in "Henry In Love", I'd've thought Colonel Blake would have been interested in younger women. Guess he's not that picky.
"Sometimes You Hear the Bullet" is refered to as a landmark episode for the series. While "Showtime" is nowhere near as good as "Bullet", it is most be certainly an important episode nonetheless. It is the first episode to have mulitiple story lines. Up 'til now, all episodes pretty much had one central story. In "Showtime" there four distinct stories being told.
Near the end of the scene at the back of the ambulance, Frank comments about Hawkeye humiliating the Major in public. Hawkeye says, "Don't forget your hat" and hands Frank a bedpan. Burns' hat can be seen behind the doctor in the ambulance.
This episode is the last time we see Ugly John. We do see his twin brother, Muldoon, later on, though. 
The USO accordion player's hair is too long for the Fifties.
This episode marks the first time Father Mulcahy would question the value of his presence at 4077th. The topic would come up at least twice more throughout the rest of M*A*S*H's run.
The picture of Frank's mother is still not in the box by the door to the Swamp. In this episode, there's a canteen in it.
In "Sometimes You Hear the Bullet", Hawkeye almost performs the series' first open heart massage. That honor falls to Trapper John in this episode.
"(Although I want to know how he managed to make the showers do that!)" - Khaja
My guess is that Frank is just outside the shower tent, manipulating the controls. Beyond that, your guess is as good as mine.
Trapper states in this ep that he started out as an architect. He switched because he couldn't handle the math. Wonder if Pernell Roberts' Trapper John ever mentioned starting out as an architect? (Then again, the Trapper John Wayne Rogers portrayed, and the one Roberts played as two different characters as far as I'm concerned.)
This episode contains the second hint that Hot Lips and Trapper may be attracted to each other. (Hawkeye: "You know those two could end up...")
Most of the time the Officers' Latrine has a sign identifying it as "Officers". However, in this ep, there are no signs on it. There is a sign a few feet away that identifies the tent and points to it, though.