I think no_slogan's will probably be the shortest, but here's some more fun with regexes at 49 chars:
  
sub reduce {
  "@{[map 1x$_,@_]}"=~/(1+)\1* \1+$/;map$_/$+[1],@_
}

[download]
Update: Here's a 48-char version that uses a relatively fast algorithim for calculating the GCM of the two numbers (I think it's attributed to Euclid?):
  
sub reduce {
  ($x,$y)=@_;($x,$y)=($y%$x,$x)while$x;map$_/$y,@_
}

[download]
   MeowChow                                   
               s aamecha.s a..a\u$&owag.print

In reply to (MeowChow) Re: (Golf) Fraction Reduction by MeowChow
in thread (Golf) Fraction Reduction by Masem

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