I thought I could easily adapt Benchmark::Thread::Size to use forks, but there is more to it than I can easily fix right now. This will probably need new versions of both forks and Benchmark::Thread::Size. In the meantime, I'm posting the result of using threads on Mac OS X:

$ perl5.8.2-threaded -MBenchmark::Thread::Size
Performing each test 10 times
(ref) 10 100
  #   (ref)                                                           
+ 
  0    1730 ± 6
  1    2085 ± 6
  2    2374 ± 6
  5    3235 ± 6
 10    4664    
 20    7536 ± 4
 50   16144 ± 2
100   30489 ± 8
[download]

I'll post the result using forks as a response to this node.

Liz