Excellent stuff Rick! Multi platform/language users must be VERY careful with default definitions and conventions. Even when different software agree,
there is danger that a classic textbook that a user has learned the subject or memorized a formula from has employed a different convention. Here is a few more
examples of conventions that may cause trouble:

Two simple
- ARIMA models: Convention on the sign of parameters for the printed estimates but also for simulation routines.
- Likelihood value: is the constant included? This may affect AIC, BIC!

and two more involved
- Definition of the autocovariance function of a multivariate stationary time series Some software may print G(h), some others may print G(-h) (recall, in the multivariate case G(h)!=G(-h)).
- Negative sign and in the complex exponent and/or constant term of discrete Fourier transform affecting the results of FFT routines. This may very affect the periodogram.