As Alan said, that is a MAJOR problem this side of the great pond, our GFCIs are rated 30mA or 100mA, but Alan's 500mA trips on thunderstorms, as do ours. It's so bad that the current wiring regulations here (our version of the NEC) highly recommend *NOT* using one for the main.
A time delayed type might be less prone to nuisance tripping, but individual circuit protection is IMHO far less inconvenient, it also gives you a fighting chance of finding out where a ground fault is without having to dismember the panel.
