Personally I think using caffiene is a crap idea, for weight loss. Sure it may give you a little more energy in the gym if you take some before, but overall it gives you uneven energy levels through the day, which can only be bad. As you "come down" you feel weak and tired, and this can make you hungry... (this thread is about weight loss, remember)

... and it can interfere with your sleep, leaving you tired through the day, unwilling to exercise & craving sugary foods to give you energy... (this thread is about weight loss...)

That's my experience anyway.