muscle building, no. For muscle building, you shouldnt be touching the same muscle in a week, much less later that day, once its torn down, it needs to heal, which is when growth occurs. Healing time is different for everyone, but a good rule of thumb is 5 days minimum.
Absolutely right. However, a carefully built workout program that works a different set of muscles with hi-intensity in each workout could benefit from 2-a-days.
For instance, a program where you lift 3x/week in 2-a-days, and do cardio 3x a week in a single longer workout:
Mon Morn: Quads, Calves 30 min workout (not including warmup)
Mon nite: Biceps, triceps 30 min workout
Tuesday: cardio - swimming 1Hr of laps
Wed Morn: Glutes, Lower back 30 min
Wed Eve: Neck, abs/obliques
Thursday: Cardio - run stairs 1H
Fri morn: chest, shoulders
Fri night: upper back
Saturday: cardio - Running 1Hr at moderate pace (6-7 min miles)
Combine something like this with enough protein, proper nutrition, and sleep and you'd get in good shape pretty fast. Although it's hard to get most ppl to work a body part hard enough once a week to really burn it in these short workouts, it can be done.
With this kind of program, you hit each body part once a week.