when do you really need a 64bit cpu?

[hanasaki]

when do you really need a 64bit cpu?

So... I pose this question.  When do you really need a 64bit CPU <other 
than the obvious potential need of a megasever needing the address 
space>?  Most of the folks I know that have an Opteron or Athlon64 do 
not have any 64bit specific software, except maybe the Linux kernel compile.

The Duron and Athlon32/Barton both seem to be replaced by the single 
Sempron32.