I like my integrated BC,
and, generally speaking, the concept of slipping weights
inside the BC’s attached, Velcro-fastened pockets works
just fine. The guy who has to heft it back on the dive
boat may not appreciate it as much, although in tropical
waters I only add six pounds of weight to my U.S. Diver
Alcyone BC’s specially designed pockets, which allow a
diver to ditch weight in an emergency by pulling a cord.
While it’s never been a big problem, I have lost lead
  from these pouches when an exceptionally high giant
  stride loosened the Velcro holding the weights in. For
  reader Dave Guccione, however, losing weights has
  become a big problem: not only do the weights fall out
  of his Genesis Phantom BC with giant strides from 6
  feet or higher, but they’ve also fallen out at depth when
  he’s been swimming horizontally.  
Guccione spent some time discussing his problem with
  Genesis’ sales rep. When we heard from Guccione, he
  had a few tips that may help those of you who use
  integrated BCs.
  - Use soft weights in integrated weight pouches. Hard
    lead weights slide around in the pouches, weakening
  the grip of the Velcro.
- Make a pouch check part of the buddy check before
    entering the water.
- Check your weight pouches often during a dive to
    see if they have slipped or been pulled loose when you
    brushed up against some object or person.
- Be judicious about the amount of weight inserted
    into the pouch.
- Don’t put all your eggs in one basket: distribute
    weights among the pouches. That way, if you do lose
    one at depth, there is less chance that the loss will
    precipitate an out-of-control ascent.
— John Q. Trigger