For every reason you might want a pseudonym in the first place, you might also want a "pseudonym from your pseudonym," especially if you use it a lot.
A specific example: I am presently running a survey of drug prices, and suggested that respondents might wish to reply through penet. Unfortunately, I realized that I could not respond to these messages without blowing my penet pseudonym. Fortunately, I had never actually used it, so I could safely "blow it". At present, if I need another penet pseudonym, I guess I'll create it through mail games. But IWBNI there were a built-in way to do this -- particularly for those who aren't able to hack mailers, who are the ones who really need a service such a penet in the first place.
Eric
PGP 2 key by finger or e-mail Eli ebrandt@jarthur.claremont.edu