Somebody asked this about weight painting in Blender last thread.
You can enable the options in armature and you can edit the mesh when it's posed. Click an vert under the "Item" tab in edit mode and you can see the bones that affect this vert. In my related pic, it has .2 in weight attached to Right leg, I adjust that to 0 or increse weight of left leg to fix the weight on this vert.
This is way easier then doing the weight painting in weight paint mode imo.
All I have done is transfered weights from my Avatars Body to the Pants mesh, now I adjust the verts in "Problem Areas" and it looks way better.