I'm strenuously disagreeing with the 75%, especially in terms of usage. Almost all nouns that end in -a (unless they're Greek neuters), -ión, -umbre, or -dad are feminine. Otherwise, they're masculine.

There are plenty of exceptions, but 1/1000 words sounds about right to me.

edit: my point was that French is far more chaotic than that, and it does cause mistakes. Goes with the general observation that French is easy enough to read, but hard to write.