There is a lot of good science behind barefoot running which the VFF try to mimic. But you can't just buy a pair of shoes thinking its a cool fad and expect not to have any problems.
For some of the science check out: http://www.barefootrunning.fas.harvard.edu/
VFF provide foot protection but not support. The idea is that if you are running correctly (on the balls of your feet) your calf and foot muscles stretch to absorb the impact that your cushy heel pads, knees and hips would absorb if you were running with a heel strike in regular running shoes.
So if you have knee problems while running these are a useful alternative, but not because they are magic shoes. Because to not hurt your feet more you have to change your running style to land on your toes (fore foot/midfoot strike). You can do that with regular running shoes, VFF, barefoot shoes, and anything that has some flexibility in the soul.
Warning, running in this manner tires your calves and arches out faster, so if you don't gradually build up the strength of these muscles you can get tendinitis.