While it works as documented in Pickaxe ( If pattern is omitted, the
value of $; is used. If $; is nil (which is the default), str is split
on whitespace as if ` ' were specified. ) I do find this behaviour
somewhat surprising:

    irb(main):004:0> "a b".split(" ")
    => ["a", "b"]
    irb(main):005:0> "a\tb".split(" ")
    => ["a", "b"]
    irb(main):006:0> "a b".split(/ /)
    => ["a", "b"]
    irb(main):007:0> "a\tb".split(/ /)
    => ["a\tb"]
    irb(main):008:0> 

I think "a\tb".split(" ") => ["a", "b"] is quite counterintuitive...

% ruby -v
ruby 1.8.1 (2003-12-25) [i386-freebsd5.1]
% 

regards,
Tom