James-

Good question.

It really does depend what you're
doing, and what niches you're into.

The sticking point is gender- some
niches will respond better to a particular
gender.

So you may want to use a female pen
name to go into a niche which is
targeting women...

But that presents its own problems...

Writing emails/salescopy in the female
voice will be tricky unless you're an
accomplished copywriter, for example.

So basically, it depends what you plan
to do online.

Good luck

-David Raybould