I don't mind people having a joint email address for a couple (OK, I do, but I can let that be) -- but using that address for a professional consultancy just seems like mixing the messages too freely.

I guess people view their email identity as part of their psyche these days. I even received an email from someone defending the professionalism of using an aol.com address. After we exchanged a couple of messages, he turned out to be a great guy, but the imputation that his e-front-door looked kindergartenish kind of stung him at first.