> What's your platform?

Guess I should have mentioned that :) Again, but with full 
version/release/platform tag:

mark@imac% /usr/bin/ruby -ve 'puts sprintf("%08b",0)'
ruby 1.6.8 (2002-12-24) [powerpc-darwin7.0]
00000000
mark@imac% /usr/local/bin/ruby -ve 'puts sprintf("%08b",0)'
ruby 1.9.0 (2004-02-14) [powerpc-darwin]
11111110