The basic idea of someone fighting mobs in bear form is, as mentioned by one earlier in the thread, pulling around three mobs and swiping them to death. Assuming you have primal fury 2/2 (100% +5 rage, per crit) it is actually very viable for taking on multiple mobs, relativley quickly.
Swipe costs 15 rage, each of its three hits has a chance to crit, because of this you have a chance to get back 0, 5, 10, or even 15 rage per swipe, in addition to your auto attacks' rage gain (which also has a chance to crit for +5 rage as well) and rage from the damage of 3 mobs. Swipe then has a good probability of costing you less than 15 rage (and occasionally free,) because of all the rage gain from the swipes, auto attack, and damage taken, bear form can produce large amounts of rage, allowing for very liberal use of swipe and other skills.
Cat form, while I love it to death, has some dissadvantages that bear form does not. Like rogues, cat form becomes "weaker and weaker" the longer the battle lasts, because of the instant attacks reliance on energy. The main idea of rogues, and a druid that prefers to fight in cat form, is to kill something quickly, they are both very potent fighters at the beggining of a fight, but the longer it takes, the less and less effective they become. Cat Form along with rogues, need to wait for energy to recover 20 every 2 seconds (with some exceptions due to some pieces of equipment,) where as the bear (and warriors) become more and more potent the longer a battle lasts, since rage is constantly building from attacks and damage taken, the Rage cost of abilities can be easily offset by the Rage gain.
Some situations Cat Form is much more efficient, but Bear Form certainly has many benefits and the potential to be just as much of a destructive force as a Cat.