I bought the XM weather system from Control Vision last year. On a
recent 8-day meandering trip through the midwest, I did flight planning
the evening before, entering the new flight plan into the PDA. You can
add default winds from the winds aloft forecast to get a good estimate
of time enroute plus heading and course info. I felt that this was
very convenient.

I found the nexrad unreliable - I visually spotted rain showers and
flew through some that never showed up on nexrad. Admittedly, they
were light and highly localized.

Inflight METARS have been very useful.