want to argue from experience?

[GJC@MIT-OZ]

Those who would want to try out their code first hand to see what
"Common-Lisp" might do to it could use NIL on some of the local VAX's.
Other things such as incompatible "/" function and readtable have
interesting effects.  You can also see what happens to numerical code
in cases which were previously errors, such as (SQRT -1) which now
returns #C(0.0 1.0), a complex number.

Another problem area is the changes to the semantics of property list
functions, which are unfortunately not completely specified!

As of now I am trying to track down some subtle Macsyma bugs (not causing
errors, just wrong results) which might be due to differences that I
did not predict beforehand. Its a lot of fun, really.

-gjc

p.s. EMACS remains the same!