Just out of interest, is there a performance penalty on NetBSD when 
   executing 32-bit binaries with 64-bit kernel, as opposed to native 
   64-bit binaries? What about Solaris, does it use the same principles 
   when executing 32-bit binaries?


every application is different.  if you care about performance you
need to actually measure 32 vs 64 bit.  depending on the application
either one can be a clear winner, or perhaps it makes no difference.