Before you consider going on a weight-loss/muscle building program ...

[get big or die mirin]

... Know that how much these people writing sugarcoat their program and try and sound 'scientific', they are all trying to sell something.
This is obvious to most people but then again I hear family members and friends asking about "would this 12 week program work for me?"

I just wanna say this: Any program that promises results in 12 weeks, or has the name 'shortcut' in it or 'secret', is not worth getting.
THERE IS NO SHORTCUT TO CONSISTENCY

More often than not, these programs are advertised in magazines and sites - these sites and magazines are there to sell you something. That's the whole point of fitness magazines. They make absolutely RIDICULOUS claims saying that you can pack on 10 kilos of solid muscle in 12 weeks and torch away that body fat! No. You can't. Even on steroids, packing on 10kg of muscle (that's 22lb) in 12 weeks is impossible.
Reading on through the programs, there's always the supplement section. For example, on bodybuilding.com, the 12 week Daily Hardcore Trainer by Kris Gethin has you taking an absurd amount of supplements; he goes on holiday and he takes his pills in a goddamn tackle box! L-Carnitine, BCAAs, L-Glutamine, Vitargo, Hydroxycut, Green Tea Extract, Casein - all UNNECESSARY.
If you want to take supplements, sort your diet out first. If you're falling short on protein throughout the day, you'll probably find it easier to incorporate a protein powder. Which one doesn't matter - but don't fall into the trap of paying more money for Casein, which these suppliers will tell you is slow digesting which you must take before bed to stop muscle tissue breaking down. It's all false.
The only supplements I recommend are fish oil tablets, a whey isolate (if you find it easier to hit your protein requirements), creatine (this can have different effects on people. I personally don't feel 'anything' taking creatine or a multivitamin for that matter), and, if you really wanna track your water intake, having a flavoured BCAA can help you chug down water, even when you're not thirsty.

The diet and workout regime of these programs - can they work? Sure. Is it an efficient way to hit your goal? Depending on how you look at it, yes.
Some people even pay money to buy these programs.
One of the biggest problems with people buying programs is that more often than not, these programs have you severely restricted in food choices, which can often lead into a binge when the person either finishes the diet or, more than likely, doesn't finish it.
Another point to mention is that because these programs are short and promise results in a short amount of time, the person doing it hasn't learned enough about nutrition and the fundamentals of calorie intake to turn it into a lifestyle after finish the program.
They may say, "oh, this salmon is healthy, it was cooked in a good oil", and eat a ton of 'healthy' foods, but wind up going into a surplus, hence gaining weight and be confused to their weight gain.
And one of the worse things, aside from a heavily restricted diet, is the sheer amount of exercise time.
If you don't know this program, google up Greg Plitt's MFT28 - absolutely RIDICULOUS. 2 workouts a day, 6, SIX, LIQUID meals, consisting of an enormous amount of SUPPLEMENTS, and only ONE solid meal a day. I know I say overtraining doesn't exist, but twice a day is nothing short of ludicrous.
You DON'T need to spend hours in a gym every day. You don't need to 'shock' your muscles. Your muscles only know one thing: if it's lifting a heavy weight. If you lift the same weight day in day out, it's going to get easy for you. Progressively overload the bar each workout, if you're a beginner, and you can expect tremendous strength (and muscle) gains.
If you want to shock your muscles, drive to the gym, stay in the car for 20 minutes, then drive back home.

You wanna lose weight? Eat at a deficit, hit your minimum fat and protein intake, stimulate your muscles to preserve muscle.

Wanna gain muscle and not gain too much fat? Eat a slight surplus, hit minimum fat and protein intake, stimulate your muscles through a strength program or a split, dependant on your goals and rest to build muscle.

Wanna gain muscle and maximize strength and not worry about getting fat? Same as above, except you eat everything in sight. You can often end up going double over maintenance.

No charge for these "plans"^ btw.

[Bigbazz]

I did P90x (a 3 month training/diet program) in 2011 (and am currently doing it again), got the videos for free and followed it without needing to do any thinking at all. In 3 months all 3 of the people I did it with including myself had become fitter, stronger and lost weight as we had wanted. One of my friends went from 11stone ish down to 9 stone and looked like bruce lee or something, he was always muscular anyway though, this just trimmed the fat. I went from 15.5 stone down to 12 stone.

I worked out around 1 hour a day 6 days a week and roughly followed their diet guidelines. Thing with programs like this is that you don't need to make it a big part of your life, you don't need to read up on diet macros and invest time into the science of it. It's all good making the extra effort if you want the extra results but for people who are looking for something to give them average but positive results without much thinking involved these videos/programs do the job.

I lost just over 3 stone (42 lbs) in 3 months, when I started I was really unfit and overweight. When I finished I was pretty fit, my endurance had increased greatly (in doing weights/body wieght exercises and cardio), I was a lot more flexible (from Yoga), I didn't gain much muscle (if any?) since obviously it's hard to do that while losing weight but I was able to lift heavier weights than before without issue.

Basically, even if it wasn't as ideal as doing it the proper way it certaintly did the job for me.

[Oblett]

Have to disagree that eating double over maintenence calories on a bulk without gaining fat. Unless you have a wicked fast metabolism or are extremely active, you will gain a lot of muscle, but a lot of fat as well. The best strategy is to adjust your calories for a 2-3lb weight increase each month (slow bulk). This way you can gain some muscle and not have to spend 6 months cutting after your bulk (which can also delay your long term muscle building goals.).