I like the concept - really nice. It would be cool to see an update of Calculize use a math library instead of JavaScript numbers.

    In Calculize:
    a = 1/3
    show a+a+a+a+a+a == 6*a
    # => false
    show pow 9,18
    #         => 150094635296999140
    # should be: 150094635296999121
    show 150094635296999122 - 150094635296999121
    # => 0

    In Python 2.6.1:
    >>> p = 1.0/3.0
    >>> p+p+p+p+p+p == 6*p
    False
    >>> pow(9,18)
    150094635296999121
    >>> 150094635296999122 - 150094635296999121
    1

These minuscule rounding errors are inconsequential for most apps, but for math...

Maybe the results will also vary between browsers, because EcmaScript talks of implementation-dependent approximation's.

[Edit: Oops, python got me with it's own quirk - division needs to be from the __future__ or it's integer]