[claudius]

It seems to work in part. For /dev/urandom, I see always roughly the same throughput:

  $ time dd if=/dev/urandom of=/dev/null bs=1 count=10000000
  real	0m10.640s
  user	0m0.696s
  sys	0m9.940s

  $ time (for i in $(seq 1 50); do dd if=/dev/urandom of=/dev/null bs=1 count=200000 2>/dev/null & done; wait)
  real	0m11.199s
  user	0m1.232s
  sys	0m42.828s

  $ time (for i in $(seq 1 500); do dd if=/dev/urandom of=/dev/null bs=1 count=20000 2>/dev/null & done; wait)
  real	0m11.234s
  user	0m1.252s
  sys	0m42.536s

whereas for /dev/zero:

  $ time dd if=/dev/zero of=/dev/null bs=1 count=10000000
  real	0m3.268s
  user	0m0.660s
  sys	0m2.604s

  $ time (for i in $(seq 1 50); do dd if=/dev/zero of=/dev/null bs=1 count=200000 2>/dev/null & done; wait)
  real	0m2.550s
  user	0m1.192s
  sys	0m8.760s

  $ time (for i in $(seq 1 500); do dd if=/dev/zero of=/dev/null bs=1 count=20000 2>/dev/null & done; wait)
  real	0m2.612s
  user	0m1.228s
  sys	0m8.112s

Of course, the bash for-loop here together with the forking has some considerable overhead, so these values should likely be interpreted carefully (Linux 3.14-rc7, Core i5 520M).