Before:

$ irb
irb(main):001:0> RUBY_DESCRIPTION
=> "ruby 1.9.0 (2007-12-25 revision 14709) [i686-linux]"
irb(main):002:0> "\u00a0"
=> " "
irb(main):003:0> "\u00a0".encoding
=> #<Encoding:UTF-8>
irb(main):004:0>

Now:

$ irb
irb(main):001:0> RUBY_DESCRIPTION
=> "ruby 1.9.0 (2008-01-28 revision 0) [i686-linux]"
irb(main):002:0> "\u00a0"
=> "\xC2\xA0"
irb(main):003:0> "\u00a0".encoding
=> #<Encoding:ASCII-8BIT>
irb(main):004:0>

- Sam Ruby