It depends on the intensity of your weightlifting sessions. Some people talk during their workouts and take 5 minutes break between each set and they almost fall asleep on the bench. They lose all the benefits of physical activities.
If your intensity level is low, do also some cardio sessions to burn more calories.
If it's high intensity, no need to do cardio.
If you only wanna do weightlifting and in a way that is optimum for burning more calories, try circuit training, which is series of multiple exercises each working different muscles simultanously with almost no rest between each. With 25 reps series instead of 8-12.
If your primary goal is to build lean mass, then I heard no cardio at all is ideal; only lift heavy weights, eat, rest.
If your primary goal is to lose weight, weightlifting at moderate intensity is still kind of cardio, so as long as you eat less than you should, you're gonna lose weight, and still build muscles at same time (the body can use the calories from bodyfat to build new muscles, as long as there's enough proteins in your diet)
I guess 3 cardio sessions of 30 minutes per week is not too much.
Doing 1h30 of cardio 5 days/week would be too much.
And preferably, do the cardio on different days then weightlifting, or at least 6 hours before if the same day.
But all this is theories.
The HIT system (http://en.wikipedia.org/wiki/High_intensity_training
) merges cardio and weightlifting in the same exercices and it seems to work. Actors from the movie "300" built their physiques using this method.