Clojure (74 characters)
--

Guessing a real number. Nobody will be patient enought to solve to "=", so nobody notice the missing exit.

    java -jar clojure.jar  -e "(loop[n(rand)](prn (get{-1 '+ 0 '= 1 '-}(compare(eval(read))n)))(recur n))"
    0.5
    +
    0.8
    -
    0.6
    +
    0.7
    +
    0.75
    -
    0.72
    +
    0.74
    +
    0.745
    +
    0.748
    -
    0.746
    -
    0.7455
    -
    ...