This is an interesting thread - and it's got me wondering if perhaps I'm not doing things right.
I work out 3 days a week, but I don't focus on one area of the body - I pretty much do the same workout every day.
My normal routine:
15 minutes on the treadmill at 4 MPH = 1 mile at a brisk walk
chest press
abs
shoulder press
leg extensions
seated row
leg curls
bicep curls
thigh isolator
more abs
tricep extensions
All told, I'm usually in the gym an hour - 15 min. on the treadmill; 45 min. of exercising.
Basically, I alternate between upper body and lower body muscles. I do 2 sets of 10 (approximately - to fatigue)
Whatever I'm doing - I've lost about 25 pounds in the past 5 months since I started. I'm not getting much bigger muscles, but they're toned better now. I'm not trying to sculpt my body - just get into shape (too many birthdays will do that to you

).
So - it seems to working, but it would be interesting to know if I could be getting better results.