I did a little more cleanup on my program, and rearranged
things so that timings of each algorithm are printed out
together. Here's the output from the Windows computer in
my office:

Randomization
  Array size:  2500     Trials: 100     Time:    0.19 ms.
  Array size:  5000     Trials: 100     Time:    0.32 ms.
  Array size: 10000     Trials: 100     Time:    0.61 ms.
  Array size: 20000     Trials: 100     Time:    1.23 ms.

Quicksort
  Array size:  2500     Trials:  50     Time:    0.32 ms.
  Array size:  5000     Trials:  50     Time:    0.68 ms.
  Array size: 10000     Trials:  50     Time:    1.44 ms.
  Array size: 20000     Trials:  50     Time:    3.02 ms.

Insertion Sort
  Array size:  2500     Trials:  20     Time:    5.60 ms.
  Array size:  5000     Trials:  20     Time:   19.84 ms.
  Array size: 10000     Trials:  20     Time:   76.20 ms.
  Array size: 20000     Trials:  20     Time:  292.05 ms.

Bubble Sort
  Array size:  2500     Trials:  10     Time:   24.19 ms.
  Array size:  5000     Trials:  10     Time:   92.78 ms.
  Array size: 10000     Trials:  10     Time:  377.15 ms.
  Array size: 20000     Trials:  10     Time: 1521.37 ms.

Here's a second set of results, same program, from my
dual-core Macintosh at home. The important point isn't
that one is faster than the other, but that the pattern
of results is the same.

Randomization
  Array size:  2500     Trials: 100     Time:    0.11 ms.
  Array size:  5000     Trials: 100     Time:    0.11 ms.
  Array size: 10000     Trials: 100     Time:    0.22 ms.
  Array size: 20000     Trials: 100     Time:    0.44 ms.

Quicksort
  Array size:  2500     Trials:  50     Time:    0.24 ms.
  Array size:  5000     Trials:  50     Time:    0.46 ms.
  Array size: 10000     Trials:  50     Time:    0.96 ms.
  Array size: 20000     Trials:  50     Time:    2.04 ms.

Insertion Sort
  Array size:  2500     Trials:  20     Time:    1.34 ms.
  Array size:  5000     Trials:  20     Time:    3.58 ms.
  Array size: 10000     Trials:  20     Time:   13.34 ms.
  Array size: 20000     Trials:  20     Time:   57.73 ms.

Bubble Sort
  Array size:  2500     Trials:  10     Time:    9.83 ms.
  Array size:  5000     Trials:  10     Time:   39.03 ms.
  Array size: 10000     Trials:  10     Time:  158.94 ms.
  Array size: 20000     Trials:  10     Time:  641.99 ms.

Here's one more set of results. What is different, and why?

Quicksort
  Array size:  2500     Trials:  50     Time:    5.53 ms.
  Array size:  5000     Trials:  50     Time:   21.84 ms.
  Array size: 10000     Trials:  50     Time:   87.72 ms.
  Array size: 20000     Trials:  50     Time:  359.35 ms.

Insertion Sort
  Array size:  2500     Trials:  20     Time:    0.27 ms.
  Array size:  5000     Trials:  20     Time:    0.23 ms.
  Array size: 10000     Trials:  20     Time:    0.47 ms.
  Array size: 20000     Trials:  20     Time:    1.04 ms.

Bubble Sort
  Array size:  2500     Trials:  10     Time:    5.82 ms.
  Array size:  5000     Trials:  10     Time:   22.01 ms.
  Array size: 10000     Trials:  10     Time:   88.55 ms.
  Array size: 20000     Trials:  10     Time:  358.27 ms.